data.json

{
  "CN": [
    {
      "q": "In a star topology, what is the single point of failure?",
      "opts": [
        "Any one cable segment",
        "The central device (hub/switch)",
        "The end nodes",
        "There is no single point of failure"
      ],
      "ans": 1,
      "exp": "If the central device fails, the entire star network fails; a single cable failure only disconnects one node."
    },
    {
      "q": "Which topology forms a single continuous path with no central server, used in SONET/SDH networks?",
      "opts": [
        "Bus",
        "Mesh",
        "Ring",
        "Tree"
      ],
      "ans": 2,
      "exp": "Ring topology connects each node to exactly two neighbours forming a continuous loop; SONET and SDH are classic examples."
    },
    {
      "q": "A fully connected mesh of n nodes requires how many point-to-point links?",
      "opts": [
        "n",
        "n-1",
        "n(n-1)/2",
        "n^2"
      ],
      "ans": 2,
      "exp": "Each node connects to every other node: nC2 = n(n-1)/2 links, which is why mesh cabling cost is high."
    },
    {
      "q": "Tree topology is best described as a combination of which two topologies?",
      "opts": [
        "Star and ring",
        "Star and bus",
        "Bus and mesh",
        "Ring and mesh"
      ],
      "ans": 1,
      "exp": "Tree (expanded star) topology connects multiple star networks to a single backbone bus, typically using Ethernet."
    },
    {
      "q": "In bus topology, when a device transmits data, the data is:",
      "opts": [
        "Sent only to the recipient's port",
        "Sent to all devices attached to the bus",
        "Sent to the central hub only",
        "Buffered in the bus controller"
      ],
      "ans": 1,
      "exp": "The bus is a shared communication medium; the transmitted signal reaches every attached device, which then discards it if not addressed to itself."
    },
    {
      "q": "What is the main drawback of a bus topology?",
      "opts": [
        "Requires a central switch",
        "Cannot handle broadcast traffic",
        "If the bus is damaged, the whole network fails",
        "Cabling cost is very high"
      ],
      "ans": 2,
      "exp": "The central cable is a single point of failure; any damage to the bus brings down the entire network."
    },
    {
      "q": "Mesh topology has two variants. Which is correct?",
      "opts": [
        "Fully and partially connected mesh",
        "Star mesh and bus mesh",
        "Wired and wireless mesh",
        "Rooted and rootless mesh"
      ],
      "ans": 0,
      "exp": "Fully connected mesh: every node connected to every other. Partially connected mesh: not all pairs are directly linked."
    },
    {
      "q": "Which topology results when a star topology is connected to a different topology?",
      "opts": [
        "Extended star",
        "Hybrid",
        "Mesh",
        "Tree"
      ],
      "ans": 1,
      "exp": "Combining different topologies produces a hybrid topology; joining two star topologies just yields another star."
    },
    {
      "q": "If the 'main bus' in a tree topology breaks:",
      "opts": [
        "Only leaf nodes are affected",
        "Only the root star is affected",
        "The whole network gets damaged",
        "Traffic is automatically rerouted"
      ],
      "ans": 2,
      "exp": "Tree topology depends on the main bus/backbone; damage to it brings the whole network down."
    },
    {
      "q": "Which network type would connect branch offices of a company across cities of a country?",
      "opts": [
        "LAN",
        "MAN",
        "WAN",
        "PAN"
      ],
      "ans": 2,
      "exp": "A WAN spans wide geographical areas such as cities and countries; a MAN is limited to a single metropolitan city."
    },
    {
      "q": "What is the approximate range limit of a PAN (Personal Area Network)?",
      "opts": [
        "Up to 10 metres",
        "Up to 100 metres",
        "Up to 1 kilometre",
        "Up to 10 kilometres"
      ],
      "ans": 0,
      "exp": "A PAN's range limit is roughly 10 metres — Bluetooth-style personal device networks."
    },
    {
      "q": "A CAN (Campus Area Network) is best described as:",
      "opts": [
        "A network within a single building",
        "A connection of devices within a campus linking multiple departments",
        "A country-wide backbone",
        "A satellite-based network"
      ],
      "ans": 1,
      "exp": "A CAN links devices across a campus area (e.g., a university) covering multiple departments/buildings."
    },
    {
      "q": "Which network uses satellites to connect devices over the global area?",
      "opts": [
        "WAN",
        "MAN",
        "GAN",
        "VPN"
      ],
      "ans": 2,
      "exp": "A GAN (Global Area Network) uses satellite links to provide worldwide connectivity."
    },
    {
      "q": "A HAN (House Area Network) is essentially:",
      "opts": [
        "A satellite home service",
        "A LAN used within a house to connect home devices",
        "A branch of a WAN",
        "A wireless PAN only"
      ],
      "ans": 1,
      "exp": "A HAN is a LAN restricted to household use, connecting PCs, printers, phones and other home devices."
    },
    {
      "q": "A VPN is best described as:",
      "opts": [
        "A private LAN with encrypted switches",
        "A private WAN built over the public internet using a secure tunnel",
        "A firewall configuration",
        "A dedicated leased line between offices"
      ],
      "ans": 1,
      "exp": "A VPN creates a secure, encrypted tunnel across the public internet, giving remote users/offices private-network access cheaply compared to dedicated WAN links."
    },
    {
      "q": "Which VPN type is intended for remote/mobile individual employees rather than connecting whole office networks?",
      "opts": [
        "Site-to-Site VPN",
        "Intranet VPN",
        "Extranet VPN",
        "Access VPN"
      ],
      "ans": 3,
      "exp": "Access (remote-access) VPN serves telecommuters and mobile users; Site-to-Site (Intranet/Extranet) links entire office networks."
    },
    {
      "q": "An Intranet VPN is used to:",
      "opts": [
        "Connect an organisation to its customers securely",
        "Connect remote offices in different geographical locations using shared infrastructure with the same policies as a private WAN",
        "Provide dial-up connectivity",
        "Encrypt internal LAN traffic only"
      ],
      "ans": 1,
      "exp": "Intranet VPN links remote offices of the same organisation via shared infrastructure, giving them WAN-like unified accessibility policies."
    },
    {
      "q": "An Extranet VPN differs from an Intranet VPN because it:",
      "opts": [
        "Uses no encryption",
        "Connects the organisation with external partners, suppliers, or customers via dedicated connections",
        "Runs only on satellite links",
        "Is limited to a single building"
      ],
      "ans": 1,
      "exp": "Extranet VPNs extend the intranet infrastructure to external stakeholders using dedicated, controlled connections."
    },
    {
      "q": "An IPv4 address is how many bits long, arranged as how many octets?",
      "opts": [
        "16 bits, 2 octets",
        "32 bits, 4 octets",
        "64 bits, 8 octets",
        "128 bits, 16 octets"
      ],
      "ans": 1,
      "exp": "IPv4 addresses are 32-bit values written as four 8-bit octets (each 0–255)."
    },
    {
      "q": "The IPv4 address 200.45.10.9 belongs to which class?",
      "opts": [
        "Class A",
        "Class B",
        "Class C",
        "Class D"
      ],
      "ans": 2,
      "exp": "Class C spans 192.0.0.0 – 223.255.255.255; used for local area networks."
    },
    {
      "q": "Which IPv4 class is reserved for multicasting?",
      "opts": [
        "Class B",
        "Class C",
        "Class D",
        "Class E"
      ],
      "ans": 2,
      "exp": "Class D (224.0.0.0 – 239.255.255.255) is reserved for multicast; Class E is kept for study/R&D."
    },
    {
      "q": "Which range covers Class A IPv4 addresses?",
      "opts": [
        "0.0.0.0 – 127.255.255.255",
        "128.0.0.0 – 191.255.255.255",
        "192.0.0.0 – 223.255.255.255",
        "240.0.0.0 – 255.255.255.254"
      ],
      "ans": 0,
      "exp": "Class A: 0.0.0.0 to 127.255.255.255, used for very large networks."
    },
    {
      "q": "Which statement about public vs private IP addresses is correct?",
      "opts": [
        "Private IPs are routable on the internet directly",
        "Public IPs are assigned by the ISP and used on the internet; private IPs are not valid on the internet without NAT/proxy",
        "Public and private IPs are interchangeable",
        "Private IPs are only IPv6"
      ],
      "ans": 1,
      "exp": "Public IPs come from the ISP and are internet-routable; private IPs need NAT or a proxy to reach the internet."
    },
    {
      "q": "Which OSI layer converts data into frames, attaches MAC addresses, and performs flow/error control on a link?",
      "opts": [
        "Physical",
        "Data link",
        "Network",
        "Transport"
      ],
      "ans": 1,
      "exp": "Framing, physical addressing, flow control, error control and link management are data-link-layer functions."
    },
    {
      "q": "Routing, logical addressing, packetizing and fragmentation are functions of which OSI layer?",
      "opts": [
        "Data link",
        "Network",
        "Transport",
        "Session"
      ],
      "ans": 1,
      "exp": "The network layer determines the best source-to-destination route, assigns logical (IP) addresses, packetizes data and fragments packets."
    },
    {
      "q": "Which OSI layer is called the 'Translation layer' and handles data compression and encryption?",
      "opts": [
        "Session",
        "Presentation",
        "Application",
        "Transport"
      ],
      "ans": 1,
      "exp": "The presentation layer translates between application format and common network format, and handles character code translation, compression and encryption."
    },
    {
      "q": "Which OSI layer transmits the raw bitstream over a physical medium?",
      "opts": [
        "Physical",
        "Data link",
        "Network",
        "Application"
      ],
      "ans": 0,
      "exp": "The physical layer is the lowest layer, handling unstructured raw-bit transmission over cables/wireless media."
    },
    {
      "q": "Beginning, maintaining and ending communication sessions between devices is the job of which layer?",
      "opts": [
        "Transport",
        "Session",
        "Presentation",
        "Application"
      ],
      "ans": 1,
      "exp": "The session layer establishes, maintains and terminates sessions between users, and reports errors from upper layers."
    },
    {
      "q": "A connection-oriented transmission where the receiver sends an acknowledgement is provided by which OSI layer?",
      "opts": [
        "Data link",
        "Network",
        "Transport",
        "Session"
      ],
      "ans": 2,
      "exp": "The transport layer offers both connection-oriented (ack-based) and connectionless services and handles end-to-end error checking."
    },
    {
      "q": "The application layer of OSI enables the user to access the network. Which is a valid application-layer protocol?",
      "opts": [
        "ARP",
        "Ethernet",
        "HTTP",
        "IP"
      ],
      "ans": 2,
      "exp": "HTTP, SMTP, DNS, FTP are all application-layer protocols; ARP is network-layer-adjacent, Ethernet is data-link, IP is network."
    },
    {
      "q": "The TCP/IP reference model has how many layers, and which layer 'holds the architecture together' by delivering IP packets?",
      "opts": [
        "4 layers; Internet layer",
        "4 layers; Transport layer",
        "5 layers; Network layer",
        "7 layers; Network layer"
      ],
      "ans": 0,
      "exp": "TCP/IP has 4 layers (Link, Internet, Transport, Application); the Internet layer (IP, ICMP) delivers packets end-to-end."
    },
    {
      "q": "In the TCP/IP model, which layer decides which physical links (e.g., serial lines, Ethernet) meet the needs of the connectionless internet layer?",
      "opts": [
        "Link layer",
        "Internet layer",
        "Transport layer",
        "Application layer"
      ],
      "ans": 0,
      "exp": "The Link layer chooses link technology (Ethernet, Sonet, etc.) to satisfy the connectionless Internet layer above it."
    },
    {
      "q": "Which statement about HTTP vs HTTPS is correct?",
      "opts": [
        "HTTP uses port 443; HTTPS uses port 80",
        "HTTPS adds SSL/TLS on top of HTTP and uses port 443 by default",
        "HTTP is stateful; HTTPS is stateless",
        "HTTPS works over UDP for speed"
      ],
      "ans": 1,
      "exp": "HTTPS is HTTP secured with SSL/TLS encryption, default port 443; plain HTTP is a stateless application-layer protocol on port 80."
    },
    {
      "q": "HTTP is called a 'stateless protocol' because:",
      "opts": [
        "It cannot carry data",
        "Each command is independent of previous commands",
        "It cannot use TCP",
        "It cannot handle cookies"
      ],
      "ans": 1,
      "exp": "Stateless means the server treats every HTTP command as unrelated to earlier ones; state must be added externally (e.g., cookies)."
    },
    {
      "q": "What does DNS primarily do?",
      "opts": [
        "Assigns IP addresses dynamically to hosts",
        "Maps domain names to their IP addresses",
        "Encrypts traffic between browser and server",
        "Routes packets between autonomous systems"
      ],
      "ans": 1,
      "exp": "DNS resolves human-readable domain names into IP addresses. Dynamic IP assignment is DHCP's job."
    },
    {
      "q": "A DNS forwarder is used when:",
      "opts": [
        "A client wants to bypass DNS caching",
        "A DNS server forwards queries it cannot resolve to external DNS servers",
        "A router converts MAC to IP addresses",
        "A server load-balances HTTP requests"
      ],
      "ans": 1,
      "exp": "A forwarder-configured DNS server passes unresolvable queries to external DNS servers for resolution."
    },
    {
      "q": "Which underlying transport does DNS typically use for its lookups?",
      "opts": [
        "TCP only",
        "UDP for standard queries",
        "ICMP",
        "SCTP"
      ],
      "ans": 1,
      "exp": "DNS uses UDP for the vast majority of queries (fast, connectionless) and falls back to TCP for large responses/zone transfers."
    },
    {
      "q": "SMTP listens on which port, and what is it used for?",
      "opts": [
        "Port 21; file transfer",
        "Port 25; transmitting email between servers",
        "Port 53; name resolution",
        "Port 110; receiving email on client"
      ],
      "ans": 1,
      "exp": "SMTP (Simple Mail Transfer Protocol) governs email transmission and is always listening on port 25."
    },
    {
      "q": "SMTP supports which two delivery methods?",
      "opts": [
        "Push and pull",
        "End-to-End and Store-and-Forward",
        "Circuit-switched and packet-switched",
        "Best-effort and reliable"
      ],
      "ans": 1,
      "exp": "SMTP supports both End-to-End (direct) and Store-and-Forward (via intermediate servers) email delivery."
    },
    {
      "q": "POP3 is responsible for:",
      "opts": [
        "Sending mail between servers",
        "Accessing the mail service on a client machine",
        "Encrypting mail in transit",
        "Routing mail through DNS"
      ],
      "ans": 1,
      "exp": "POP3 (Post Office Protocol v3) handles retrieving mail to a client machine, operating in Delete or Keep modes."
    },
    {
      "q": "Which is a key difference between TCP and UDP?",
      "opts": [
        "UDP is connection-oriented; TCP is connectionless",
        "TCP retransmits lost packets; UDP does not",
        "UDP provides flow control and acknowledgements",
        "TCP is faster than UDP"
      ],
      "ans": 1,
      "exp": "TCP is connection-oriented with error checking, ACKs, flow control and retransmission; UDP is faster, simpler, and connectionless."
    },
    {
      "q": "Which protocol does 'basic checksum-only' error checking?",
      "opts": [
        "TCP",
        "UDP",
        "SMTP",
        "HTTP"
      ],
      "ans": 1,
      "exp": "UDP has only checksum-based error detection; TCP performs extensive error checking with retransmissions and flow control."
    },
    {
      "q": "Which protocol auto-assigns IP addresses and other network configuration to devices?",
      "opts": [
        "ARP",
        "DHCP",
        "DNS",
        "ICMP"
      ],
      "ans": 1,
      "exp": "DHCP (application layer) auto-configures IP, subnet mask and DNS details for hosts (default port 67)."
    },
    {
      "q": "ARP is used to:",
      "opts": [
        "Map an IP address to a MAC address",
        "Map a MAC address to an IP address",
        "Find the best route using hop count",
        "Report network-layer errors"
      ],
      "ans": 0,
      "exp": "Address Resolution Protocol converts a logical (IP) address into the device's physical (MAC) address on the local network."
    },
    {
      "q": "Which protocol is primarily used for error handling and diagnostics (e.g., 'ping')?",
      "opts": [
        "ARP",
        "ICMP",
        "RIP",
        "FTP"
      ],
      "ans": 1,
      "exp": "ICMP (Internet Control Message Protocol) is a network-layer protocol used by routers for error reporting and connectivity diagnostics."
    },
    {
      "q": "RIP (Routing Information Protocol) selects the best route based on:",
      "opts": [
        "Bandwidth",
        "Link delay",
        "Hop count",
        "Packet loss"
      ],
      "ans": 2,
      "exp": "RIP is a dynamic routing protocol that uses hop-count as its metric; suited to small/medium networks."
    },
    {
      "q": "FTP is used to:",
      "opts": [
        "Send email",
        "Transfer files reliably between hosts",
        "Look up domain names",
        "Assign IP addresses"
      ],
      "ans": 1,
      "exp": "FTP (File Transfer Protocol) is an application-layer protocol for reliable, efficient file transfer, including downloads from remote servers."
    },
    {
      "q": "Which statement about MAC and IP addresses is correct?",
      "opts": [
        "Both are assigned by the ISP",
        "MAC identifies the physical device (from the NIC manufacturer); IP identifies the network connection (from the ISP)",
        "MAC changes with every network; IP is permanent",
        "IP is a 48-bit hardware address"
      ],
      "ans": 1,
      "exp": "NIC manufacturers assign MAC addresses (hardware identity); ISPs assign IP addresses (network identity)."
    },
    {
      "q": "Hub vs switch — which is correct?",
      "opts": [
        "Hub is data-link and filters packets",
        "Switch is physical and broadcasts to all ports",
        "Hub is physical with no packet filtering; switch is data-link with packet filtering",
        "Both operate at the network layer"
      ],
      "ans": 2,
      "exp": "A hub blindly repeats signals to every port (physical layer, no filtering); a switch is a full-duplex data-link-layer device that filters and forwards frames per port."
    },
    {
      "q": "A node that connects two or more networks and forwards messages between them is called:",
      "opts": [
        "Repeater",
        "Bridge",
        "Gateway/router",
        "Modem"
      ],
      "ans": 2,
      "exp": "Gateways/routers connect different networks, regulating and forwarding traffic between them."
    },
    {
      "q": "A NIC (Network Interface Card):",
      "opts": [
        "Is a router",
        "Is a peripheral card that attaches a PC to a network and has its own MAC address",
        "Is a software firewall",
        "Is a DNS server"
      ],
      "ans": 1,
      "exp": "A NIC connects a PC to a network and carries a unique MAC address identifying that PC on the network."
    },
    {
      "q": "When you type google.com, what happens immediately after the OS resolves the IP via DNS?",
      "opts": [
        "The browser renders the cached page",
        "An HTTP request is sent without any connection",
        "A TCP connection is established with the server using a three-way handshake",
        "The server pushes the page via UDP"
      ],
      "ans": 2,
      "exp": "After DNS resolution: TCP three-way handshake → HTTP request → HTTP response → render (and cache if cacheable)."
    },
    {
      "q": "Which delivery method targets a subset of nodes with the same data (used to send data to multiple selected receivers)?",
      "opts": [
        "Unicast",
        "Anycast",
        "Multicast",
        "Broadcast"
      ],
      "ans": 2,
      "exp": "Multicast targets a subset of receivers. Unicast: one node; anycast: any one of several servers; broadcast: all nodes."
    },
    {
      "q": "Which delivery method sends data to any one of several servers (used by CDNs)?",
      "opts": [
        "Unicast",
        "Anycast",
        "Multicast",
        "Broadcast"
      ],
      "ans": 1,
      "exp": "Anycast routes traffic to the topologically nearest instance among several, commonly used by CDNs and DNS root servers."
    },
    {
      "q": "A firewall's role is to:",
      "opts": [
        "Assign IP addresses",
        "Monitor incoming/outgoing traffic and block based on security policies",
        "Compress network packets",
        "Route between VLANs only"
      ],
      "ans": 1,
      "exp": "A firewall (hardware, software, or both) sits between a private network and the public internet, enforcing security policies."
    },
    {
      "q": "VPN encrypts internet traffic to:",
      "opts": [
        "Increase raw speed",
        "Disguise online identity and protect confidentiality",
        "Reduce packet loss",
        "Improve DNS lookups"
      ],
      "ans": 1,
      "exp": "A VPN protects confidentiality and hides the user's real IP/identity; it does not inherently increase throughput."
    },
    {
      "q": "Which are the elements of a protocol?",
      "opts": [
        "Syntax, semantics, timing",
        "Header, body, footer",
        "Encoding, error correction, addressing",
        "Encryption, integrity, availability"
      ],
      "ans": 0,
      "exp": "A protocol is defined by syntax (format), semantics (meaning), and timing (when/how fast data is sent)."
    },
    {
      "q": "Network reliability is measured by all of these EXCEPT:",
      "opts": [
        "Downtime",
        "Failure frequency",
        "Catastrophe handling",
        "Colour of the cabling"
      ],
      "ans": 3,
      "exp": "Reliability metrics per the notes: downtime (recovery time), failure frequency, and catastrophe robustness."
    },
    {
      "q": "Subnetting a network is done primarily to:",
      "opts": [
        "Reduce hardware cost",
        "Achieve higher routing efficiency and enhance security",
        "Force devices to use IPv6",
        "Speed up ARP resolutions"
      ],
      "ans": 1,
      "exp": "Subnetting divides a network into subnets, improving routing efficiency and security, and reducing routing-table lookup time."
    },
    {
      "q": "Netstat is a utility that:",
      "opts": [
        "Configures IP addresses",
        "Shows current TCP/IP connections and settings",
        "Encrypts traffic",
        "Restarts network interfaces"
      ],
      "ans": 1,
      "exp": "Netstat is a command-line utility providing useful information about the current TCP/IP setting and active connections."
    },
    {
      "q": "Which command is used on Linux/UNIX/macOS to view and configure network interfaces?",
      "opts": [
        "ipconfig",
        "ifconfig",
        "tracert",
        "ping"
      ],
      "ans": 1,
      "exp": "ifconfig (Interface Configuration) is used on Linux/UNIX/macOS; ipconfig is the Windows equivalent."
    },
    {
      "q": "RAID stands for:",
      "opts": [
        "Random Access Independent Disks",
        "Redundant Array of Independent Disks",
        "Reliable Array of Integrated Devices",
        "Redundant Access to Internal Data"
      ],
      "ans": 1,
      "exp": "RAID = Redundant Array of Independent Disks — stores data redundantly across multiple drives for performance/fault tolerance (7 levels)."
    }
  ],
  "OS": [
    {
      "q": "An operating system is best defined as:",
      "opts": [
        "Application software for productivity tasks",
        "An interface between the user/applications and hardware, managing resources",
        "A database management system",
        "A network protocol suite"
      ],
      "ans": 1,
      "exp": "The OS is the interface between users/applications and hardware, responsible for process execution, resource allocation, CPU, file and memory management."
    },
    {
      "q": "In which OS type does the CPU switch to another job whenever the running process waits for I/O?",
      "opts": [
        "Batch OS",
        "Multiprogramming OS",
        "Real-time OS",
        "Time-sharing OS"
      ],
      "ans": 1,
      "exp": "Multiprogramming keeps several jobs in main memory; when the running process blocks for I/O, the OS assigns the CPU to another job."
    },
    {
      "q": "A time-sharing OS is characterised by:",
      "opts": [
        "Batch execution without interaction",
        "Interaction with the user (e.g., keyboard) with the OS responding to instructions",
        "Fixed deadlines only",
        "Serial execution of jobs"
      ],
      "ans": 1,
      "exp": "Time-sharing systems interact with users through input devices; the OS executes instructions and responds with output."
    },
    {
      "q": "A Real-Time OS is typically used when:",
      "opts": [
        "Multiple users share a computer casually",
        "Rigid, fixed timing constraints govern operations",
        "Batch jobs must be queued",
        "Cost-cutting is the priority"
      ],
      "ans": 1,
      "exp": "Real-time systems have well-defined, fixed time constraints — used in dedicated systems that must meet deadlines."
    },
    {
      "q": "In a batch OS, a job is assigned to the CPU:",
      "opts": [
        "When the previous job's execution completes",
        "On a time slice",
        "Based on I/O availability",
        "At user request"
      ],
      "ans": 0,
      "exp": "Batch OS stores similar jobs in memory; a new job takes the CPU only after the previous one finishes execution."
    },
    {
      "q": "Each process in an OS is represented by:",
      "opts": [
        "A page table",
        "A Process Control Block (PCB)",
        "A file descriptor",
        "A kernel thread"
      ],
      "ans": 1,
      "exp": "A PCB stores metadata about a process — including the program counter — used by the OS to manage the process."
    },
    {
      "q": "The program counter (PC) of a process indicates:",
      "opts": [
        "Number of instructions executed",
        "Address of the next instruction to be executed",
        "CPU utilisation percentage",
        "Process priority"
      ],
      "ans": 1,
      "exp": "The PC value indicates the address of the next instruction of the process being executed."
    },
    {
      "q": "A process makes 4 fork() system calls. How many child processes are created?",
      "opts": [
        "4",
        "8",
        "15",
        "16"
      ],
      "ans": 2,
      "exp": "n fork() calls generate 2^n − 1 children: 2^4 − 1 = 15."
    },
    {
      "q": "If Completion Time = 27 and Arrival Time = 5, Burst Time = 12, what is the Waiting Time?",
      "opts": [
        "22",
        "10",
        "12",
        "15"
      ],
      "ans": 1,
      "exp": "Turnaround = 27 − 5 = 22; Waiting = Turnaround − Burst = 22 − 12 = 10."
    },
    {
      "q": "Turnaround Time is defined as:",
      "opts": [
        "Burst time − Arrival time",
        "Completion time − Arrival time",
        "Completion time − Burst time",
        "Waiting time + Burst time"
      ],
      "ans": 1,
      "exp": "Turnaround Time = Completion Time − Arrival Time."
    },
    {
      "q": "Waiting Time is defined as:",
      "opts": [
        "Turnaround − Burst",
        "Burst − Turnaround",
        "Arrival − Burst",
        "Completion + Arrival"
      ],
      "ans": 0,
      "exp": "Waiting Time = Turnaround Time − Burst Time."
    },
    {
      "q": "Which resources does a thread NOT share with other threads of the same process?",
      "opts": [
        "Code section",
        "Data section",
        "Open files and signals",
        "Its own stack and register set"
      ],
      "ans": 3,
      "exp": "Each thread has its own PC, register set, and stack; it shares the process's code, data, files and signals."
    },
    {
      "q": "Which pair is a valid classification of threads?",
      "opts": [
        "Primary and secondary threads",
        "User threads and kernel threads",
        "Static and dynamic threads",
        "Local and remote threads"
      ],
      "ans": 1,
      "exp": "Threads are broadly user threads (implemented by user libraries) and kernel threads (implemented by the OS)."
    },
    {
      "q": "Which of these is NOT typically an advantage of multithreaded programming?",
      "opts": [
        "Enhanced responsiveness",
        "Resource sharing within a process",
        "Economical use of resources",
        "Guaranteed deadlock avoidance"
      ],
      "ans": 3,
      "exp": "Multithreading is responsive, economical, shares process resources and exploits multiprocessors, but does not itself prevent deadlocks."
    },
    {
      "q": "Which scheduling algorithm is the simplest and schedules based purely on arrival times?",
      "opts": [
        "FCFS",
        "SJF",
        "Round Robin",
        "HRRN"
      ],
      "ans": 0,
      "exp": "First Come First Serve is the simplest algorithm; jobs are scheduled strictly in arrival order."
    },
    {
      "q": "Shortest Remaining Time First (SRTF) is:",
      "opts": [
        "Non-preemptive version of FCFS",
        "Preemptive version of SJF",
        "Priority scheduling",
        "Round-robin variant"
      ],
      "ans": 1,
      "exp": "SRTF preempts the running process if a newly arrived process has a shorter remaining burst — the preemptive form of SJF."
    },
    {
      "q": "Round Robin scheduling gives each process:",
      "opts": [
        "Priority based on burst",
        "A fixed time slice in a cyclic order",
        "Only I/O time",
        "Non-preemptive execution"
      ],
      "ans": 1,
      "exp": "RR assigns each process a fixed time quantum in a cyclic fashion, giving fair sharing among all processes."
    },
    {
      "q": "In non-preemptive priority scheduling, if two processes have equal priority, the tiebreaker is:",
      "opts": [
        "Random selection",
        "Arrival time",
        "Burst time",
        "Process ID"
      ],
      "ans": 1,
      "exp": "For equal priorities, scheduling defaults to arrival order."
    },
    {
      "q": "Which scheduling algorithm avoids starvation via a response ratio?",
      "opts": [
        "SJF",
        "Round Robin",
        "HRRN",
        "MLFQ"
      ],
      "ans": 2,
      "exp": "HRRN = (Waiting + Burst) / Burst — long waits raise the ratio, so long-waiting processes eventually get scheduled."
    },
    {
      "q": "In Multilevel Feedback Queue scheduling, a process that consumes too much CPU time is:",
      "opts": [
        "Terminated",
        "Moved to a higher-priority queue",
        "Moved to a lower-priority queue",
        "Given a longer quantum in the same queue"
      ],
      "ans": 2,
      "exp": "MLFQ demotes CPU-hungry processes to lower-priority queues based on CPU-burst behaviour, unlike static MLQ."
    },
    {
      "q": "Which is NOT one of the three required conditions for a valid critical-section solution?",
      "opts": [
        "Mutual exclusion",
        "Progress",
        "Bounded waiting",
        "Circular wait"
      ],
      "ans": 3,
      "exp": "Solutions require mutual exclusion, progress, and bounded waiting. Circular wait is a deadlock condition."
    },
    {
      "q": "A race condition is:",
      "opts": [
        "A process running faster than expected",
        "When the final output depends on the order in which shared variables are accessed",
        "Two processes with equal priorities",
        "Blocking on I/O for too long"
      ],
      "ans": 1,
      "exp": "Race conditions arise when the outcome depends on interleavings of accesses to shared variables."
    },
    {
      "q": "Bounded waiting guarantees:",
      "opts": [
        "A process waits at most a fixed amount of wall-clock time",
        "A bound exists on how many times other processes can enter the CS after one has requested it",
        "No process ever waits",
        "Waiting equals burst time"
      ],
      "ans": 1,
      "exp": "Bounded waiting ensures a limit on how many times other processes may enter the critical section between a process's request and its grant."
    },
    {
      "q": "A semaphore whose value ranges over an unrestricted integer domain is a:",
      "opts": [
        "Binary semaphore",
        "Counting semaphore",
        "Mutex",
        "Spinlock"
      ],
      "ans": 1,
      "exp": "Counting semaphores take unrestricted integers; binary semaphores take only 0/1 and implement mutual exclusion."
    },
    {
      "q": "Binary semaphores are used to implement:",
      "opts": [
        "Deadlock avoidance",
        "Mutual exclusion and process synchronisation",
        "Priority scheduling",
        "Paging"
      ],
      "ans": 1,
      "exp": "Binary semaphores (values 0/1) implement mutual exclusion and synchronise concurrent processes."
    },
    {
      "q": "A mutex differs from a counting semaphore in that:",
      "opts": [
        "A mutex has integer value",
        "A mutex provides mutual exclusion — only one thread can hold it at a time",
        "Semaphores cannot be shared",
        "Mutex is only used in kernels"
      ],
      "ans": 1,
      "exp": "A mutex is a mutual-exclusion primitive; only one owner holds it at a time, generalisable via semaphores."
    },
    {
      "q": "Which set lists all four necessary conditions for deadlock?",
      "opts": [
        "Mutual exclusion, hold & wait, preemption, circular wait",
        "Mutual exclusion, hold & wait, no preemption, circular wait",
        "Starvation, hold & wait, no preemption, aging",
        "Mutual exclusion, race condition, no preemption, circular wait"
      ],
      "ans": 1,
      "exp": "Deadlock requires all four simultaneously: mutual exclusion, hold and wait, NO preemption, circular wait."
    },
    {
      "q": "Windows and UNIX generally handle deadlock by:",
      "opts": [
        "Banker's algorithm",
        "Deadlock detection and recovery",
        "Ignoring the problem (Ostrich approach)",
        "Wait-die scheme"
      ],
      "ans": 2,
      "exp": "Since deadlock is rare, both Windows and UNIX ignore it and rely on a reboot — the 'ignore altogether' strategy."
    },
    {
      "q": "Banker's algorithm is a technique for:",
      "opts": [
        "Deadlock detection",
        "Deadlock avoidance",
        "Deadlock recovery",
        "Starvation prevention"
      ],
      "ans": 1,
      "exp": "Banker's algorithm avoids deadlock — never allocating resources such that a safe sequence cannot be found."
    },
    {
      "q": "The 'Hold and Wait' condition means:",
      "opts": [
        "Processes only wait, never hold resources",
        "A process holds at least one resource while waiting for more",
        "Resources are held permanently",
        "Resources are never released"
      ],
      "ans": 1,
      "exp": "Hold and wait: a process is holding at least one resource while requesting additional resources."
    },
    {
      "q": "Overlays are best described as:",
      "opts": [
        "Fixed-size memory partitions",
        "Only keeping in memory the instructions/data needed at a given time",
        "A page replacement algorithm",
        "A form of paging"
      ],
      "ans": 1,
      "exp": "Overlays load only the instructions/data currently needed, letting a program larger than memory execute."
    },
    {
      "q": "Swapping in multiprogramming refers to:",
      "opts": [
        "Moving a process out of memory when its time slice ends",
        "Swapping CPU cores",
        "Exchanging register values",
        "Compacting free memory"
      ],
      "ans": 0,
      "exp": "Swapping moves processes that have used their time slice out of memory to disk to make room for others."
    },
    {
      "q": "In variable-partition allocation, which strategy leaves the LARGEST leftover hole after allocation?",
      "opts": [
        "First fit",
        "Best fit",
        "Worst fit",
        "Next fit"
      ],
      "ans": 2,
      "exp": "Worst fit deliberately places the process in the hole that leaves the maximum gap."
    },
    {
      "q": "First fit allocates:",
      "opts": [
        "The smallest hole that fits",
        "The largest hole",
        "The first hole in which the process fits completely",
        "A hole at random"
      ],
      "ans": 2,
      "exp": "First fit scans free holes in order and allocates the first hole into which the process fits completely."
    },
    {
      "q": "Best fit chooses the hole that:",
      "opts": [
        "Leaves the maximum gap",
        "Fits the process with the minimum leftover space",
        "Is at the highest address",
        "Was most recently freed"
      ],
      "ans": 1,
      "exp": "Best fit selects the hole in which the process fits with the least memory left over."
    },
    {
      "q": "External fragmentation in contiguous allocation is primarily solved by:",
      "opts": [
        "Overlays",
        "Swapping",
        "Paging",
        "Compaction of registers"
      ],
      "ans": 2,
      "exp": "Paging removes the requirement of contiguous allocation by dividing memory into equal-size frames/pages."
    },
    {
      "q": "Internal fragmentation occurs in systems that use:",
      "opts": [
        "Variable-size allocation units",
        "Fixed-size allocation units",
        "Segmentation only",
        "Linked allocation"
      ],
      "ans": 1,
      "exp": "Fixed-size units (fixed partitions, pages) waste space inside an allocated block. Variable-size units cause external fragmentation."
    },
    {
      "q": "Segmentation differs from paging in that:",
      "opts": [
        "Segments are equal-sized",
        "Segmentation provides a user view; the logical address space is a collection of segments (of varying sizes)",
        "Segmentation cannot use paging",
        "Segmentation eliminates page faults"
      ],
      "ans": 1,
      "exp": "Segmentation is user-oriented: logical space is a collection of variable-length segments; it may or may not use paging underneath."
    },
    {
      "q": "A page fault is:",
      "opts": [
        "An error when a program accesses an invalid address",
        "An interrupt raised when a referenced page is in the virtual space but not in physical memory",
        "A disk read error",
        "A TLB parity error"
      ],
      "ans": 1,
      "exp": "A page fault is a hardware interrupt when a referenced page is mapped in virtual memory but not present in physical memory."
    },
    {
      "q": "Belady's anomaly refers to:",
      "opts": [
        "More page faults with more frames under LRU",
        "More page faults with more frames under FIFO",
        "Fewer page faults with fewer frames under Optimal",
        "Thrashing at high multiprogramming levels"
      ],
      "ans": 1,
      "exp": "Under FIFO replacement, more frames can paradoxically increase page faults (Belady's anomaly)."
    },
    {
      "q": "Why is the Optimal page replacement algorithm not used in practice?",
      "opts": [
        "It causes Belady's anomaly",
        "It requires future knowledge of the reference string",
        "It has the highest fault rate",
        "It needs special hardware"
      ],
      "ans": 1,
      "exp": "Optimal replaces the page not used for the longest time in the FUTURE, which an OS cannot know; it serves as a benchmark."
    },
    {
      "q": "LRU replaces the page that:",
      "opts": [
        "Was loaded first",
        "Will not be used for the longest time in the future",
        "Was least recently used",
        "Has the highest reference count"
      ],
      "ans": 2,
      "exp": "LRU replaces the least recently used page, based on past access history."
    },
    {
      "q": "Virtual memory allows:",
      "opts": [
        "Only kernel code to execute",
        "Processes to execute even when they cannot fit entirely in physical memory",
        "Multiple OS instances to coexist",
        "Faster CPU access than caches"
      ],
      "ans": 1,
      "exp": "Virtual memory enables processes to execute outside of memory — larger than physical RAM allows."
    },
    {
      "q": "Demand paging specifies that:",
      "opts": [
        "All pages are always in memory",
        "If a memory region is not being used, it is swapped to disk to make room for other applications",
        "Pages are pre-fetched sequentially",
        "Kernel code cannot be paged"
      ],
      "ans": 1,
      "exp": "Demand paging swaps out unused memory regions to disk so applications can use RAM they need now."
    },
    {
      "q": "Disk Access Time equals:",
      "opts": [
        "Seek time + transfer time",
        "Rotational latency + transfer time",
        "Seek time + rotational latency + transfer time",
        "Seek time × rotational latency"
      ],
      "ans": 2,
      "exp": "Access time = seek + rotational latency + transfer time."
    },
    {
      "q": "Seek time is:",
      "opts": [
        "Time for the sector to rotate under the head",
        "Time to position the disk arm on the desired track",
        "Time to transfer bytes",
        "Total disk response time"
      ],
      "ans": 1,
      "exp": "Seek time is the time to locate the disk arm on the specified track."
    },
    {
      "q": "Rotational latency is:",
      "opts": [
        "Track-positioning time",
        "Time for the desired sector to rotate into position under the head",
        "Byte-transfer time",
        "Interrupt-handling time"
      ],
      "ans": 1,
      "exp": "Rotational latency is the time taken for the desired sector to rotate into a readable position."
    },
    {
      "q": "Which disk scheduling algorithm behaves like an elevator?",
      "opts": [
        "FCFS",
        "SSTF",
        "SCAN",
        "CLOOK"
      ],
      "ans": 2,
      "exp": "SCAN moves the arm in one direction servicing requests, reverses at the end, and services on the return — the elevator algorithm."
    },
    {
      "q": "SSTF schedules requests based on:",
      "opts": [
        "Arrival order",
        "Shortest seek time from the current head position",
        "Priority level",
        "Track number"
      ],
      "ans": 1,
      "exp": "SSTF (Shortest Seek Time First) picks the request nearest to the current head position, minimising seek time."
    },
    {
      "q": "How does LOOK improve upon SCAN?",
      "opts": [
        "Services requests in arrival order",
        "Reverses at the last pending request instead of travelling to the disk's physical end",
        "Always jumps to the far end",
        "Uses shortest seek time"
      ],
      "ans": 1,
      "exp": "LOOK avoids the wasted traversal to the disk edge by reversing direction at the last request in front of the head."
    },
    {
      "q": "CLOOK differs from LOOK in that:",
      "opts": [
        "It moves in one direction and then jumps to the other end's last request rather than reversing",
        "It ignores requests behind the head",
        "It uses random ordering",
        "It only services writes"
      ],
      "ans": 0,
      "exp": "CLOOK, like CSCAN, is one-directional; after serving the last request on the way, it jumps to the last request at the other end."
    },
    {
      "q": "A kernel that contains all OS code in a single executable image is called:",
      "opts": [
        "Microkernel",
        "Monolithic kernel",
        "Macro kernel",
        "Hybrid kernel"
      ],
      "ans": 1,
      "exp": "A monolithic kernel packs all OS services into one image; microkernel runs only minimal services; macro kernel combines both."
    },
    {
      "q": "A microkernel runs:",
      "opts": [
        "All OS services in kernel space",
        "Only minimal performance-affecting services in kernel space, with the rest handled by processes",
        "No kernel services at all",
        "Only user applications"
      ],
      "ans": 1,
      "exp": "Microkernels keep the kernel small — running only minimal services — and delegate the rest to user-mode processes."
    },
    {
      "q": "Thrashing occurs when:",
      "opts": [
        "The CPU executes too many user instructions",
        "The processor spends most of its time swapping pages instead of executing instructions",
        "Too many interrupts arrive per second",
        "The disk queue is empty"
      ],
      "ans": 1,
      "exp": "Thrashing is when excessive paging in a virtual-memory system collapses useful throughput."
    },
    {
      "q": "Which technique lets multiple users share a single copy of a program if the code cannot modify itself and each user's data is stored separately?",
      "opts": [
        "Demand paging",
        "Re-entrancy",
        "Spooling",
        "Overlays"
      ],
      "ans": 1,
      "exp": "Re-entrancy is a memory-saving technique for multiprogrammed time-sharing systems."
    },
    {
      "q": "Aging is a technique used to:",
      "opts": [
        "Prevent deadlock",
        "Avoid starvation in resource scheduling",
        "Reduce internal fragmentation",
        "Speed up context switching"
      ],
      "ans": 1,
      "exp": "Aging gradually raises the priority of long-waiting processes so they eventually get scheduled — solving starvation."
    },
    {
      "q": "Starvation in resource scheduling is:",
      "opts": [
        "A process finishing very quickly",
        "A waiting process not getting the resources it needs for a long time",
        "Two processes in a deadlock",
        "Excessive CPU utilisation"
      ],
      "ans": 1,
      "exp": "Starvation: a process waits indefinitely because resources keep being allocated to others."
    },
    {
      "q": "Spooling is most closely associated with:",
      "opts": [
        "CPU scheduling",
        "Printing — queueing multiple applications' output jobs on disk",
        "Page replacement",
        "Deadlock avoidance"
      ],
      "ans": 1,
      "exp": "Spooling temporarily gathers data (classically print jobs) on disk and queues them to the device."
    },
    {
      "q": "Logical vs physical address space:",
      "opts": [
        "Both are generated by the memory unit",
        "Logical address is generated by the CPU; physical address is seen by the memory unit",
        "Logical address is seen by hardware only",
        "Physical address is generated at compile time"
      ],
      "ans": 1,
      "exp": "Logical addresses are CPU-generated (virtual); physical addresses are what the memory unit uses."
    }
  ],
  "DBMS": [
    {
      "q": "A database is best defined as:",
      "opts": [
        "Any file on disk",
        "A collection of related data representing some aspect of the real world",
        "Only a spreadsheet",
        "A network protocol"
      ],
      "ans": 1,
      "exp": "A database is a collection of related data representing some aspect of the real world, built and populated for a certain task."
    },
    {
      "q": "Which of the following is NOT a problem of file-processing systems that DBMS was designed to solve?",
      "opts": [
        "Data redundancy and inconsistency",
        "Difficulty in accessing data",
        "Atomicity of updates",
        "Physical storage of data on disk"
      ],
      "ans": 3,
      "exp": "DBMS addresses redundancy, access difficulty, isolation, integrity, atomicity, concurrency and security. Physical storage exists in any file system."
    },
    {
      "q": "In an ER diagram, a weak entity set:",
      "opts": [
        "Has a primary key underlined with a solid line",
        "Lacks sufficient attributes for unique identification and uses a discriminator (dashed underline)",
        "Cannot participate in relationships",
        "Must have a composite primary key"
      ],
      "ans": 1,
      "exp": "A weak entity set lacks a primary key; it has a partial key (discriminator) shown with a dashed underline and depends on a strong entity."
    },
    {
      "q": "A strong entity set is one that:",
      "opts": [
        "Cannot exist without another entity",
        "Contains sufficient attributes to uniquely identify all its entities (has a primary key)",
        "Only has multi-valued attributes",
        "Has no relationships"
      ],
      "ans": 1,
      "exp": "Strong entity sets have a primary key of their own, drawn as a solid underline."
    },
    {
      "q": "A relationship set where three entity sets participate is called:",
      "opts": [
        "Unary",
        "Binary",
        "Ternary",
        "N-ary"
      ],
      "ans": 2,
      "exp": "Ternary relationship sets involve exactly three participating entity sets."
    },
    {
      "q": "A relationship set where only one entity set participates is called:",
      "opts": [
        "Unary",
        "Binary",
        "Ternary",
        "Recursive N-ary"
      ],
      "ans": 0,
      "exp": "Unary relationship sets have one participating entity set (also called recursive)."
    },
    {
      "q": "'One employee manages many departments, each managed by one employee' is which cardinality (employee → department)?",
      "opts": [
        "One-to-one",
        "One-to-many",
        "Many-to-one",
        "Many-to-many"
      ],
      "ans": 1,
      "exp": "An A-entity relates to many B-entities, while each B-entity relates to at most one A-entity — one-to-many."
    },
    {
      "q": "'Age' derived from 'Date of Birth' is an example of which attribute type?",
      "opts": [
        "Composite",
        "Multi-valued",
        "Derived",
        "Key"
      ],
      "ans": 2,
      "exp": "Derived attributes are computed from other attributes."
    },
    {
      "q": "'Name' composed of first, middle and last name is which attribute type?",
      "opts": [
        "Simple",
        "Composite",
        "Multi-valued",
        "Derived"
      ],
      "ans": 1,
      "exp": "Composite attributes are made up of several simple sub-attributes."
    },
    {
      "q": "A phone-number attribute holding multiple numbers per person is:",
      "opts": [
        "Simple",
        "Composite",
        "Multi-valued",
        "Derived"
      ],
      "ans": 2,
      "exp": "Multi-valued attributes can hold more than one value for a given entity."
    },
    {
      "q": "Which constraint states that no attribute of a primary key may be NULL?",
      "opts": [
        "Domain constraint",
        "Referential integrity",
        "Entity integrity",
        "Tuple uniqueness"
      ],
      "ans": 2,
      "exp": "Entity integrity requires primary-key attributes to be non-null."
    },
    {
      "q": "A foreign key value must:",
      "opts": [
        "Always be unique",
        "Never be NULL",
        "Either exist in the referenced relation's primary key or be NULL",
        "Be a composite attribute"
      ],
      "ans": 2,
      "exp": "Referential integrity: every foreign key is either present among the referenced primary key values or is NULL."
    },
    {
      "q": "A domain constraint specifies:",
      "opts": [
        "The set of allowed values (atomic values from a domain) for an attribute",
        "That primary keys are unique",
        "That tuples are unique",
        "That foreign keys exist"
      ],
      "ans": 0,
      "exp": "Domain constraints restrict the values (from an atomic domain) an attribute may take."
    },
    {
      "q": "Tuple uniqueness constraint specifies that:",
      "opts": [
        "All primary key values are distinct",
        "All tuples must be necessarily unique in any relation",
        "No NULLs are allowed",
        "Foreign keys must not repeat"
      ],
      "ans": 1,
      "exp": "Tuple uniqueness requires every tuple in a relation to be unique."
    },
    {
      "q": "A super key is:",
      "opts": [
        "The primary key only",
        "Any set of attributes that identifies each tuple uniquely (may include extra attributes)",
        "A minimal candidate key",
        "A foreign key"
      ],
      "ans": 1,
      "exp": "Super key: any attribute set uniquely identifying tuples; a candidate key is a minimal super key."
    },
    {
      "q": "Which key is defined as a MINIMAL set of attributes that uniquely identifies each tuple?",
      "opts": [
        "Super key",
        "Candidate key",
        "Composite key",
        "Unique key"
      ],
      "ans": 1,
      "exp": "A candidate key is a minimal super key."
    },
    {
      "q": "Candidate keys not chosen as the primary key are called:",
      "opts": [
        "Foreign keys",
        "Surrogate keys",
        "Alternate keys",
        "Partial keys"
      ],
      "ans": 2,
      "exp": "Alternate keys are the unimplemented candidate keys."
    },
    {
      "q": "A primary key made of multiple attributes is called:",
      "opts": [
        "Composite key",
        "Foreign key",
        "Alternate key",
        "Super key"
      ],
      "ans": 0,
      "exp": "Composite key: primary key composed of multiple attributes."
    },
    {
      "q": "Which is true about a UNIQUE key (as distinct from a primary key)?",
      "opts": [
        "Cannot be NULL",
        "May have a NULL value and is non-updatable once assigned",
        "Must be composite",
        "Every table needs exactly one"
      ],
      "ans": 1,
      "exp": "Unique keys allow NULL and, per the notes, are non-updatable once assigned."
    },
    {
      "q": "A functional dependency X → Y is trivial if and only if:",
      "opts": [
        "Y ⊆ X",
        "X ⊆ Y",
        "X ∩ Y = ∅",
        "Y is a super key"
      ],
      "ans": 0,
      "exp": "Trivial FD: RHS is a subset of LHS."
    },
    {
      "q": "Non-trivial FD X → Y means:",
      "opts": [
        "Y ⊆ X",
        "At least one attribute of Y is not in X",
        "X is empty",
        "Y = X"
      ],
      "ans": 1,
      "exp": "Non-trivial: at least one RHS attribute is not in the LHS."
    },
    {
      "q": "The set of all attributes functionally determined by an attribute set is called its:",
      "opts": [
        "Domain",
        "Closure",
        "Cover",
        "Projection"
      ],
      "ans": 1,
      "exp": "The closure X+ is everything functionally derivable from X."
    },
    {
      "q": "A decomposition of R into R1…Rn is LOSSLESS when:",
      "opts": [
        "R1 ⋈ R2 ⋈ … ⋈ Rn ⊃ R",
        "R1 ⋈ R2 ⋈ … ⋈ Rn = R",
        "R1 ∪ R2 ∪ … ∪ Rn = R",
        "Each Ri is in BCNF"
      ],
      "ans": 1,
      "exp": "Lossless join: natural join of sub-relations reproduces the original."
    },
    {
      "q": "A lossy join decomposition satisfies:",
      "opts": [
        "R1 ⋈ … ⋈ Rn = R",
        "R1 ⋈ … ⋈ Rn ⊃ R",
        "R1 ⋈ … ⋈ Rn ⊂ R",
        "R1 ⋈ … ⋈ Rn is empty"
      ],
      "ans": 1,
      "exp": "Lossy join: the natural join yields extra spurious tuples (superset of R)."
    },
    {
      "q": "Dependency preservation ensures that:",
      "opts": [
        "No FDs of the original relation are lost after decomposition",
        "All tuples are preserved",
        "Only primary keys are retained",
        "Relations become atomic"
      ],
      "ans": 0,
      "exp": "Dependency preservation keeps every original FD satisfied by the decomposed sub-relations."
    },
    {
      "q": "A relation is in 1NF if:",
      "opts": [
        "It has no partial dependencies",
        "Each cell contains only an atomic (or NULL) value",
        "It has no transitive dependencies",
        "Every determinant is a super key"
      ],
      "ans": 1,
      "exp": "1NF: attribute values are atomic (single-valued) or NULL."
    },
    {
      "q": "A relation is in 2NF if it is in 1NF and has no:",
      "opts": [
        "Transitive dependency",
        "Partial dependency",
        "Multivalued dependency",
        "Join dependency"
      ],
      "ans": 1,
      "exp": "2NF removes partial dependencies — proper subsets of a candidate key determining non-prime attributes."
    },
    {
      "q": "A → B is a transitive dependency (violating 3NF) when:",
      "opts": [
        "A is a super key and B is prime",
        "A is not a super key and B is a non-prime attribute",
        "A is a candidate key",
        "B ⊆ A"
      ],
      "ans": 1,
      "exp": "3NF is violated when a non-super-key determines a non-prime attribute."
    },
    {
      "q": "BCNF requires that for every non-trivial FD A → B:",
      "opts": [
        "B is a prime attribute",
        "A is a super key",
        "A is a foreign key",
        "A and B are disjoint"
      ],
      "ans": 1,
      "exp": "BCNF: the determinant of every non-trivial FD must be a super key."
    },
    {
      "q": "Read(A) in a transaction:",
      "opts": [
        "Writes A to disk",
        "Reads A from the database into a main-memory buffer",
        "Deletes A",
        "Locks A permanently"
      ],
      "ans": 1,
      "exp": "Read(A) reads A's value from the database and stores it in the buffer in main memory."
    },
    {
      "q": "Write(A) in a transaction:",
      "opts": [
        "Reads A from disk",
        "Writes A's updated buffer value back to the database",
        "Locks A",
        "Aborts A"
      ],
      "ans": 1,
      "exp": "Write(A) writes the updated value of A from buffer to database."
    },
    {
      "q": "Which ACID property guarantees a transaction happens completely or not at all?",
      "opts": [
        "Atomicity",
        "Consistency",
        "Isolation",
        "Durability"
      ],
      "ans": 0,
      "exp": "Atomicity forbids partial transactions."
    },
    {
      "q": "Which ACID property guarantees that database integrity constraints are maintained?",
      "opts": [
        "Atomicity",
        "Consistency",
        "Isolation",
        "Durability"
      ],
      "ans": 1,
      "exp": "Consistency ensures the DB remains consistent before and after every transaction."
    },
    {
      "q": "Which ACID property ensures concurrent transactions produce the same result as some serial ordering?",
      "opts": [
        "Atomicity",
        "Consistency",
        "Isolation",
        "Durability"
      ],
      "ans": 2,
      "exp": "Isolation ensures concurrent transactions do not interfere; the outcome equals some serial execution."
    },
    {
      "q": "Durability ensures that:",
      "opts": [
        "Transactions run instantly",
        "Committed changes are permanent and survive failures",
        "Failed transactions leave no trace",
        "Undoable operations are logged"
      ],
      "ans": 1,
      "exp": "Durability persists committed changes to disk permanently, surviving any failure."
    },
    {
      "q": "A transaction enters PARTIALLY COMMITTED state when:",
      "opts": [
        "Its first instruction executes",
        "Its last instruction has executed but changes are still in the main-memory buffer",
        "Its changes are written to disk",
        "It is rolled back"
      ],
      "ans": 1,
      "exp": "After the last instruction, changes are still buffered — partially committed."
    },
    {
      "q": "A transaction enters ABORTED state after:",
      "opts": [
        "Successful commit",
        "Failure and rollback of changes",
        "Its first read",
        "Being paused"
      ],
      "ans": 1,
      "exp": "After failure the changes are undone via rollback, then the transaction is aborted."
    },
    {
      "q": "The last state in a transaction's life cycle is:",
      "opts": [
        "Committed",
        "Aborted",
        "Terminated",
        "Failed"
      ],
      "ans": 2,
      "exp": "After committed or aborted, transactions enter the terminated state — end of life cycle."
    },
    {
      "q": "Which schedules are ALWAYS consistent, recoverable, cascadeless and strict?",
      "opts": [
        "Non-serial schedules",
        "Serial schedules",
        "Concurrent schedules",
        "View serializable schedules"
      ],
      "ans": 1,
      "exp": "Serial schedules always have all four properties; non-serial ones may not."
    },
    {
      "q": "A non-serial schedule convertible to a serial one by swapping non-conflicting operations is:",
      "opts": [
        "View serializable",
        "Conflict serializable",
        "Cascadeless",
        "Strict"
      ],
      "ans": 1,
      "exp": "That is the definition of conflict serializability."
    },
    {
      "q": "A schedule where T2 dirty-reads from uncommitted T1 and commits BEFORE T1 is:",
      "opts": [
        "Recoverable",
        "Irrecoverable",
        "Strict",
        "Cascadeless"
      ],
      "ans": 1,
      "exp": "If the reader commits before the writer it depended on, no rollback can save the read — irrecoverable."
    },
    {
      "q": "A cascading schedule is one where:",
      "opts": [
        "Only one transaction runs at a time",
        "Failure of one transaction causes several dependent transactions to roll back",
        "Transactions run in reverse arrival order",
        "Reads only happen at commit"
      ],
      "ans": 1,
      "exp": "Cascading rollback: aborting one transaction cascades to others that read its dirty data."
    },
    {
      "q": "In a strict schedule, a transaction:",
      "opts": [
        "Reads freely from uncommitted data",
        "Is neither allowed to read nor write a data item until the last writer commits/aborts",
        "Only writes",
        "Only reads"
      ],
      "ans": 1,
      "exp": "Strict schedules delay both reads and writes until the previous writer commits or aborts."
    },
    {
      "q": "σ (Selection) operator:",
      "opts": [
        "Chooses columns",
        "Chooses rows satisfying a condition",
        "Joins two relations",
        "Renames a relation"
      ],
      "ans": 1,
      "exp": "Selection filters rows based on a predicate; projection filters columns."
    },
    {
      "q": "∏ (Projection) operator:",
      "opts": [
        "Chooses rows",
        "Chooses columns",
        "Sorts tuples",
        "Removes NULLs"
      ],
      "ans": 1,
      "exp": "Projection retains selected columns of a relation."
    },
    {
      "q": "Cross product of R1 (m rows) × R2 (n rows) returns how many rows?",
      "opts": [
        "m + n",
        "m − n",
        "m × n",
        "max(m,n)"
      ],
      "ans": 2,
      "exp": "Cross product yields every combination — m×n tuples."
    },
    {
      "q": "In relational algebra, minimum rows returned by R1 ∪ R2 (m,n rows) is:",
      "opts": [
        "0",
        "m + n",
        "max(m, n)",
        "min(m, n)"
      ],
      "ans": 2,
      "exp": "Union returns at least max(m, n) tuples (if one set's tuples subset the other's) and at most m + n."
    },
    {
      "q": "R1 − R2 returns at most how many rows?",
      "opts": [
        "m",
        "n",
        "m + n",
        "m − n"
      ],
      "ans": 0,
      "exp": "Difference R1 − R2 returns at most m rows (all of R1 if none are in R2)."
    },
    {
      "q": "Natural join of two relations with NO common attribute equals:",
      "opts": [
        "Union",
        "Intersection",
        "Cross product",
        "Left outer join"
      ],
      "ans": 2,
      "exp": "Without a common attribute, no equality condition exists, so natural join becomes the Cartesian product."
    },
    {
      "q": "Which operator returns tuples of A associated with EVERY tuple of B?",
      "opts": [
        "A ⋈ B",
        "A / B (division)",
        "A − B",
        "A ⟕ B"
      ],
      "ans": 1,
      "exp": "Division answers 'for all' queries; B's attributes must be a proper subset of A's."
    },
    {
      "q": "Left outer join of R and S returns:",
      "opts": [
        "Only matching tuples",
        "All tuples of R and matching tuples of S (with NULLs for unmatched S)",
        "All tuples of S only",
        "All tuples of R and S with duplicates"
      ],
      "ans": 1,
      "exp": "LEFT OUTER JOIN keeps every tuple of R; unmatched S columns are NULL."
    },
    {
      "q": "Full outer join of R and S returns:",
      "opts": [
        "Only intersection",
        "Union of all tuples of R and S with NULLs in unmatched attributes",
        "Only R",
        "Only S"
      ],
      "ans": 1,
      "exp": "FULL OUTER JOIN keeps every tuple of both R and S with NULLs where unmatched."
    },
    {
      "q": "A clustering index is created on:",
      "opts": [
        "A key field in an unordered file",
        "A non-key field on which records are physically ordered",
        "Any secondary access path",
        "A hash bucket"
      ],
      "ans": 1,
      "exp": "Clustering index is built on a non-key field on which the data file is physically ordered."
    },
    {
      "q": "A primary index is:",
      "opts": [
        "A secondary access path",
        "An ordered file with (key, block-pointer) fields, matching primary-key ordering of data",
        "An index on any non-key field",
        "An index over multiple tables"
      ],
      "ans": 1,
      "exp": "Primary index: ordered file with the primary key and a pointer to the data block containing that key."
    },
    {
      "q": "A secondary index:",
      "opts": [
        "Replaces the primary index",
        "Provides additional access paths for a file for which primary access already exists",
        "Removes indexing",
        "Is used only for range queries"
      ],
      "ans": 1,
      "exp": "Secondary indexes give additional means of accessing a file that already has primary access."
    },
    {
      "q": "Why is searching generally faster in a B+ tree than in a B tree?",
      "opts": [
        "B+ trees are always binary",
        "Non-leaf B+ nodes hold no record pointers, so they pack more keys and the tree is shallower",
        "B+ trees store data only in the root",
        "B trees do not allow range queries"
      ],
      "ans": 1,
      "exp": "B+ trees' internal nodes have higher fan-out, decreasing tree depth."
    },
    {
      "q": "The 'order' of a B-tree is:",
      "opts": [
        "The height of the tree",
        "The maximum number of children a node can have",
        "The number of keys in the root",
        "The block size"
      ],
      "ans": 1,
      "exp": "Order = maximum number of children a node can have."
    },
    {
      "q": "In a B-tree of order P, the root can have between how many children?",
      "opts": [
        "1 and P",
        "2 and P",
        "⌈P/2⌉ and P",
        "P and 2P"
      ],
      "ans": 1,
      "exp": "Per the notes, the root can have between 2 and P children."
    }
  ],
  "SQL": [
    {
      "q": "Which set of commands belongs to DDL?",
      "opts": [
        "SELECT, INSERT, UPDATE",
        "CREATE, ALTER, DROP, TRUNCATE",
        "GRANT, REVOKE",
        "COMMIT, ROLLBACK, SAVEPOINT"
      ],
      "ans": 1,
      "exp": "DDL defines schema structure: CREATE, ALTER, DROP, TRUNCATE, RENAME."
    },
    {
      "q": "Which commands belong to DML?",
      "opts": [
        "CREATE, DROP",
        "SELECT, INSERT, UPDATE, DELETE, MERGE",
        "GRANT, REVOKE",
        "COMMIT, ROLLBACK"
      ],
      "ans": 1,
      "exp": "DML manipulates data: SELECT, INSERT, UPDATE, DELETE, MERGE."
    },
    {
      "q": "GRANT and REVOKE belong to which language category?",
      "opts": [
        "DDL",
        "DML",
        "DCL",
        "TCL"
      ],
      "ans": 2,
      "exp": "DCL controls permissions."
    },
    {
      "q": "COMMIT, ROLLBACK and SAVEPOINT belong to which language category?",
      "opts": [
        "DDL",
        "DML",
        "DCL",
        "TCL"
      ],
      "ans": 3,
      "exp": "TCL controls transactions."
    },
    {
      "q": "Which command performs an UPSERT (insert or update) operation?",
      "opts": [
        "REPLACE",
        "MERGE",
        "UPDATE",
        "COALESCE"
      ],
      "ans": 1,
      "exp": "MERGE is the DML statement for UPSERT semantics."
    },
    {
      "q": "Which is the key difference between DELETE and TRUNCATE?",
      "opts": [
        "DELETE removes the table structure; TRUNCATE does not",
        "TRUNCATE removes all records and reclaims allocated space and is DDL; DELETE is DML and can use WHERE",
        "DELETE cannot be rolled back",
        "TRUNCATE can delete specific rows"
      ],
      "ans": 1,
      "exp": "TRUNCATE (DDL) removes all rows including allocated space, no WHERE; DELETE (DML) removes selected rows, structure and space intact."
    },
    {
      "q": "RENAME belongs to which category of SQL commands?",
      "opts": [
        "DDL",
        "DML",
        "DCL",
        "TCL"
      ],
      "ans": 0,
      "exp": "RENAME (renaming an object) is a DDL command per the notes."
    },
    {
      "q": "Which query returns only unique country values from Customers?",
      "opts": [
        "SELECT UNIQUE Country FROM Customers;",
        "SELECT DISTINCT Country FROM Customers;",
        "SELECT Country FROM Customers GROUP BY *;",
        "SELECT ONLY Country FROM Customers;"
      ],
      "ans": 1,
      "exp": "SELECT DISTINCT returns only different values of the listed columns."
    },
    {
      "q": "'SELECT * FROM Customers;' means:",
      "opts": [
        "Select the number of customers",
        "Select all columns of all rows in Customers",
        "Select only the first row",
        "Select all tables named Customers"
      ],
      "ans": 1,
      "exp": "* is a wildcard for all columns."
    },
    {
      "q": "How do you correctly test for NULL values?",
      "opts": [
        "WHERE Address = NULL",
        "WHERE Address == NULL",
        "WHERE Address IS NULL",
        "WHERE Address <> NULL"
      ],
      "ans": 2,
      "exp": "NULL cannot be compared with =/<>; use IS NULL / IS NOT NULL."
    },
    {
      "q": "Which is the correct 'not equal' operator in standard SQL?",
      "opts": [
        "!==",
        "<>",
        "~=",
        "<>= "
      ],
      "ans": 1,
      "exp": "Standard SQL uses <> for not-equal; some dialects also accept !=."
    },
    {
      "q": "An UPDATE statement without a WHERE clause will:",
      "opts": [
        "Fail with an error",
        "Update only the first row",
        "Update every row in the table",
        "Update no rows"
      ],
      "ans": 2,
      "exp": "Omitting WHERE applies the SET clause to all rows — a classic interview trap."
    },
    {
      "q": "A DELETE statement without a WHERE clause:",
      "opts": [
        "Fails",
        "Deletes only the first row",
        "Deletes all rows but leaves the table structure",
        "Drops the table"
      ],
      "ans": 2,
      "exp": "DELETE without WHERE removes all rows but preserves the table structure, attributes and indexes."
    },
    {
      "q": "Which clause combines conditions such that a row must satisfy ALL of them?",
      "opts": [
        "OR",
        "AND",
        "NOT",
        "IN"
      ],
      "ans": 1,
      "exp": "AND requires all connected conditions to be TRUE."
    },
    {
      "q": "The NOT operator in a WHERE clause:",
      "opts": [
        "Combines two conditions",
        "Returns rows where the condition is FALSE",
        "Sorts data",
        "Only works with NULL"
      ],
      "ans": 1,
      "exp": "NOT returns rows where the given condition is NOT TRUE."
    },
    {
      "q": "'ORDER BY Country ASC, CustomerName DESC' does:",
      "opts": [
        "Sorts by Country descending only",
        "Sorts by Country ascending, ties broken by CustomerName descending",
        "Sorts by CustomerName first",
        "Errors out"
      ],
      "ans": 1,
      "exp": "Multiple ORDER BY columns sort hierarchically left to right."
    },
    {
      "q": "By default, ORDER BY sorts:",
      "opts": [
        "Descending",
        "Ascending",
        "Randomly",
        "By primary key"
      ],
      "ans": 1,
      "exp": "Default order is ascending; use DESC for descending."
    },
    {
      "q": "Which pattern finds customer names with 'r' in the SECOND position?",
      "opts": [
        "LIKE 'r%'",
        "LIKE '%r'",
        "LIKE '_r%'",
        "LIKE '%_r'"
      ],
      "ans": 2,
      "exp": "Underscore matches exactly one char; '_r%' = any first character, 'r' second, anything after."
    },
    {
      "q": "What does 'LIKE a__%' match?",
      "opts": [
        "Names starting with 'a', at least 2 characters",
        "Names starting with 'a', at least 3 characters",
        "Names ending in 'a'",
        "Names containing 'a'"
      ],
      "ans": 1,
      "exp": "'a' + two underscores + % → at least 3 characters starting with 'a'."
    },
    {
      "q": "Which wildcard represents zero, one, or multiple characters in LIKE?",
      "opts": [
        "_",
        "*",
        "%",
        "?"
      ],
      "ans": 2,
      "exp": "% is zero-or-more characters; underscore is exactly one character."
    },
    {
      "q": "WHERE Price BETWEEN 10 AND 20 selects:",
      "opts": [
        "Prices strictly between 10 and 20 (exclusive)",
        "Prices from 10 to 20 inclusive",
        "Prices ≥ 10 only",
        "Prices ≤ 20 only"
      ],
      "ans": 1,
      "exp": "BETWEEN is inclusive of both endpoints."
    },
    {
      "q": "WHERE Country IN ('Germany','France','UK') is shorthand for:",
      "opts": [
        "Multiple AND conditions",
        "Multiple OR conditions",
        "A JOIN",
        "A subquery only"
      ],
      "ans": 1,
      "exp": "IN acts as an OR-chained equality; can also take a subquery."
    },
    {
      "q": "Which is a valid syntactic use of IN with a subquery?",
      "opts": [
        "WHERE Country IN 'Germany','France'",
        "WHERE Country IN (SELECT Country FROM Suppliers)",
        "WHERE Country IN SELECT Country FROM Suppliers",
        "WHERE Country IN Suppliers"
      ],
      "ans": 1,
      "exp": "IN accepts a value list or a SELECT statement enclosed in parentheses."
    },
    {
      "q": "Inserting without listing column names requires:",
      "opts": [
        "Values in any order",
        "Values in the same order as the table's columns, one for each",
        "Only NULLs",
        "Numeric values only"
      ],
      "ans": 1,
      "exp": "Omitting column list requires supplying values for every column in table column order."
    },
    {
      "q": "Which is the syntax to update multiple columns?",
      "opts": [
        "UPDATE t SET c1=v1 AND c2=v2 WHERE …",
        "UPDATE t SET c1=v1, c2=v2 WHERE …",
        "UPDATE t (c1,c2) VALUES (v1,v2)",
        "UPDATE t.c1=v1, t.c2=v2 WHERE …"
      ],
      "ans": 1,
      "exp": "Multiple SET assignments are separated by commas."
    },
    {
      "q": "Which aggregate returns the number of rows matching a criterion?",
      "opts": [
        "SUM()",
        "COUNT()",
        "TOTAL()",
        "ROWS()"
      ],
      "ans": 1,
      "exp": "COUNT() counts rows."
    },
    {
      "q": "MIN() returns:",
      "opts": [
        "Smallest value of the selected column",
        "Number of NULLs",
        "First inserted row",
        "Median"
      ],
      "ans": 0,
      "exp": "MIN() returns the smallest value of a column."
    },
    {
      "q": "MAX() returns:",
      "opts": [
        "Largest value of the selected column",
        "Last inserted row",
        "Highest ID",
        "Row count"
      ],
      "ans": 0,
      "exp": "MAX() returns the largest value of a column."
    },
    {
      "q": "AVG() returns:",
      "opts": [
        "Sum of numeric column",
        "Average of numeric column",
        "Median of numeric column",
        "Mode of numeric column"
      ],
      "ans": 1,
      "exp": "AVG() returns the average value of a numeric column."
    },
    {
      "q": "SUM() returns:",
      "opts": [
        "Row count",
        "Total sum of a numeric column",
        "Standard deviation",
        "Product of all values"
      ],
      "ans": 1,
      "exp": "SUM() returns the total sum of a numeric column."
    },
    {
      "q": "GROUP BY is used to:",
      "opts": [
        "Sort rows",
        "Group rows sharing values in one or more columns, typically with aggregates",
        "Filter individual rows",
        "Rename columns"
      ],
      "ans": 1,
      "exp": "GROUP BY groups rows for aggregate summaries — often used with COUNT/SUM/MIN/MAX/AVG."
    },
    {
      "q": "Why does SQL provide HAVING in addition to WHERE?",
      "opts": [
        "HAVING is faster",
        "WHERE cannot use aggregates; HAVING filters after grouping",
        "HAVING replaces GROUP BY",
        "WHERE cannot filter text"
      ],
      "ans": 1,
      "exp": "WHERE filters rows before grouping; HAVING filters after GROUP BY using aggregates."
    },
    {
      "q": "Which query lists countries having more than 5 customers?",
      "opts": [
        "SELECT Country FROM Customers WHERE COUNT(CustomerID) > 5;",
        "SELECT COUNT(CustomerID), Country FROM Customers GROUP BY Country HAVING COUNT(CustomerID) > 5;",
        "SELECT COUNT(*) FROM Customers HAVING Country > 5;",
        "SELECT Country FROM Customers GROUP BY COUNT(CustomerID) > 5;"
      ],
      "ans": 1,
      "exp": "Aggregate filtering needs GROUP BY + HAVING; COUNT in WHERE is invalid."
    },
    {
      "q": "Evaluation priority: which is given priority when both appear in a query?",
      "opts": [
        "HAVING before WHERE",
        "WHERE before HAVING",
        "They run simultaneously",
        "Depends on the index"
      ],
      "ans": 1,
      "exp": "WHERE filters individual rows first; then GROUP BY groups; then HAVING filters groups."
    },
    {
      "q": "Which JOIN returns only rows with matching values in BOTH tables?",
      "opts": [
        "LEFT JOIN",
        "RIGHT JOIN",
        "INNER JOIN",
        "FULL OUTER JOIN"
      ],
      "ans": 2,
      "exp": "INNER JOIN keeps only matched rows."
    },
    {
      "q": "In a LEFT JOIN of Customers (left) and Orders (right), a customer with no orders appears:",
      "opts": [
        "Not at all",
        "With NULLs in the Orders columns",
        "Once per existing order of others",
        "With zeros in Orders columns"
      ],
      "ans": 1,
      "exp": "LEFT JOIN retains all left-table rows; unmatched right columns are NULL."
    },
    {
      "q": "A RIGHT JOIN returns:",
      "opts": [
        "All rows from the left table",
        "All rows from the right table and matching rows from the left",
        "Only intersection",
        "Union of the two tables"
      ],
      "ans": 1,
      "exp": "RIGHT JOIN keeps every right-table row, with NULLs for unmatched left columns."
    },
    {
      "q": "A FULL OUTER JOIN returns:",
      "opts": [
        "Only matching rows",
        "All rows from either table, with NULLs where no match exists",
        "Only unmatched rows",
        "A cross product"
      ],
      "ans": 1,
      "exp": "FULL OUTER JOIN combines LEFT and RIGHT — keeps all rows of both tables with NULLs."
    },
    {
      "q": "Which conditions must SELECTs meet to be combined with UNION?",
      "opts": [
        "Same number of columns, similar data types, same column order",
        "Same table names",
        "Same WHERE clauses",
        "Identical indexes"
      ],
      "ans": 0,
      "exp": "UNION requires equal column count, compatible data types, same order."
    },
    {
      "q": "Difference between UNION and UNION ALL:",
      "opts": [
        "UNION ALL removes duplicates",
        "UNION selects only distinct values by default; UNION ALL allows duplicates",
        "UNION is faster than UNION ALL",
        "No difference"
      ],
      "ans": 1,
      "exp": "UNION deduplicates the combined result; UNION ALL preserves duplicates, so it is typically faster."
    },
    {
      "q": "Which are equivalent ways (across DB systems) to fetch the first 3 rows?",
      "opts": [
        "SELECT TOP 3 …, LIMIT 3, FETCH FIRST 3 ROWS ONLY, ROWNUM <= 3",
        "Only LIMIT 3",
        "Only SELECT TOP 3",
        "HEAD 3 and TAIL 3"
      ],
      "ans": 0,
      "exp": "SQL Server uses TOP, MySQL uses LIMIT, standard SQL/DB2/Oracle 12c+ use FETCH FIRST, older Oracle uses ROWNUM."
    },
    {
      "q": "'ALTER TABLE Customers ADD Email varchar(255);' does what?",
      "opts": [
        "Creates a new table",
        "Adds a new column Email to the existing Customers table",
        "Renames a column",
        "Inserts a row"
      ],
      "ans": 1,
      "exp": "ALTER TABLE ADD adds a column; DROP COLUMN removes; MODIFY/ALTER COLUMN changes datatype."
    },
    {
      "q": "'ALTER TABLE Customers DROP COLUMN Email;' does what?",
      "opts": [
        "Deletes the whole table",
        "Deletes the Email column from the table",
        "Removes rows where Email is NULL",
        "Renames Email"
      ],
      "ans": 1,
      "exp": "DROP COLUMN removes an entire column and its data."
    },
    {
      "q": "'ALTER TABLE Persons ALTER COLUMN DateOfBirth year;' does what?",
      "opts": [
        "Adds a new column",
        "Deletes the column",
        "Modifies the column's datatype",
        "Renames the column"
      ],
      "ans": 2,
      "exp": "ALTER/MODIFY COLUMN changes a column's data type."
    },
    {
      "q": "CREATE DATABASE is used to:",
      "opts": [
        "Create a table",
        "Create a new SQL database",
        "Grant permissions",
        "Truncate a database"
      ],
      "ans": 1,
      "exp": "CREATE DATABASE creates a new database (DDL)."
    },
    {
      "q": "DROP DATABASE:",
      "opts": [
        "Drops a table",
        "Deletes an existing SQL database",
        "Truncates rows",
        "Rolls back"
      ],
      "ans": 1,
      "exp": "DROP DATABASE removes an existing database entirely."
    },
    {
      "q": "DROP TABLE:",
      "opts": [
        "Removes all rows but keeps the table",
        "Removes the table (structure and data)",
        "Rolls back",
        "Renames the table"
      ],
      "ans": 1,
      "exp": "DROP TABLE removes the table entirely."
    },
    {
      "q": "TRUNCATE TABLE:",
      "opts": [
        "Deletes the table itself",
        "Deletes all rows but preserves the table structure",
        "Deletes rows matching a condition",
        "Renames the table"
      ],
      "ans": 1,
      "exp": "TRUNCATE removes all rows and reclaims space; table structure remains."
    },
    {
      "q": "Which TCL command permanently saves the current transaction's changes?",
      "opts": [
        "ROLLBACK",
        "COMMIT",
        "SAVEPOINT",
        "MERGE"
      ],
      "ans": 1,
      "exp": "COMMIT commits a transaction, persisting its changes."
    },
    {
      "q": "Which TCL command undoes a transaction on error?",
      "opts": [
        "ROLLBACK",
        "COMMIT",
        "SAVEPOINT",
        "GRANT"
      ],
      "ans": 0,
      "exp": "ROLLBACK reverts the transaction's changes on error."
    },
    {
      "q": "Which TCL command creates an intermediate point to roll back to?",
      "opts": [
        "COMMIT",
        "ROLLBACK",
        "SAVEPOINT",
        "CHECKPOINT"
      ],
      "ans": 2,
      "exp": "SAVEPOINT marks a point in a transaction; ROLLBACK TO savepoint undoes work after it."
    },
    {
      "q": "GRANT and REVOKE are used to:",
      "opts": [
        "Modify data",
        "Give and withdraw access privileges to database users",
        "Create tables",
        "Commit transactions"
      ],
      "ans": 1,
      "exp": "GRANT provides privileges; REVOKE withdraws them (both DCL)."
    }
  ]
}