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NIELIT BCC practice questions

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Question 1Information, Electronics and Communications Technology (IECT)

Which number system is used internally by digital computers to represent and process data?

  1. Decimal
  2. Sexagesimal
  3. Roman
  4. Binary Correct answer.

Explanation

Digital circuits have two stable voltage states, so data is stored and manipulated in base-2 (binary) form using the digits 0 and 1. Other number systems are used only for human convenience or notation.

Question 2Information, Electronics and Communications Technology (IECT)

What is the decimal equivalent of the binary number 1101?

  1. 11
  2. 13 Correct answer.
  3. 14
  4. 12

Explanation

Evaluate place values: 1×8 + 1×4 + 0×2 + 1×1 = 13. Each bit position doubles in weight from right to left.

Question 3Information, Electronics and Communications Technology (IECT)

In Boolean algebra, what is the output of a two-input AND gate when both inputs are 1?

  1. 0
  2. Undefined
  3. 1 Correct answer.
  4. High impedance

Explanation

The AND function yields 1 only when every input is 1, so with both inputs high the output is high. If any input were 0 the output would be 0.

Question 4Information, Electronics and Communications Technology (IECT)

Which logic gate produces a HIGH output only when its inputs are different?

  1. XNOR gate
  2. NOR gate
  3. XOR gate Correct answer.
  4. AND gate

Explanation

The exclusive-OR output is 1 when exactly one input is 1, that is, when the inputs differ. Its complement, XNOR, is 1 when inputs are equal.

Question 5Information, Electronics and Communications Technology (IECT)

Which memory type loses its stored contents when power is switched off?

  1. ROM
  2. Flash memory
  3. EEPROM
  4. Volatile RAM Correct answer.

Explanation

Volatile memory such as SRAM and DRAM requires continuous power to retain data. ROM, flash and EEPROM are non-volatile and keep data without power.

Question 6Information, Electronics and Communications Technology (IECT)

In the OSI reference model, which layer is responsible for end-to-end reliable delivery and flow control?

  1. Network layer
  2. Physical layer
  3. Data link layer
  4. Transport layer Correct answer.

Explanation

The transport layer provides end-to-end delivery between processes, including segmentation, flow control and error recovery. The network layer handles logical addressing and routing instead.

Question 7Information, Electronics and Communications Technology (IECT)

Which device forwards data packets between different networks using IP addresses?

  1. Router Correct answer.
  2. Hub
  3. Repeater
  4. Patch panel

Explanation

A router examines the destination IP address and selects the best path to another network. Hubs and repeaters only regenerate signals within one collision domain.

Question 8Information, Electronics and Communications Technology (IECT)

Which of the following is an example of system software?

  1. Operating system Correct answer.
  2. Spreadsheet application
  3. Web browser
  4. Photo editor

Explanation

System software manages hardware and provides a platform for applications; an operating system is the core example. Spreadsheets, browsers and editors are application software.

Question 9Information, Electronics and Communications Technology (IECT)

What is the hexadecimal equivalent of the binary number 10111110?

  1. CE
  2. BF
  3. BC
  4. BE Correct answer.

Explanation

Group the bits into nibbles: 1011 = B and 1110 = E, giving BE. Each hex digit maps to exactly four binary bits.

Question 10Information, Electronics and Communications Technology (IECT)

Which expression represents the two's complement of an 8-bit binary value?

  1. Invert all bits
  2. Subtract 1 from the value
  3. Invert all bits and then add 1 Correct answer.
  4. Add 1 to the value

Explanation

Two's complement is formed by complementing every bit and adding one to the least significant bit. This representation lets subtraction be performed by addition.

Question 11Information, Electronics and Communications Technology (IECT)

A 4-input multiplexer has how many select lines?

  1. 4
  2. 1
  3. 3
  4. 2 Correct answer.

Explanation

A multiplexer with 2^n data inputs needs n select lines, so 4 inputs require 2 select lines. These lines choose which data input reaches the single output.

Question 12Information, Electronics and Communications Technology (IECT)

Which flip-flop is most commonly used to build synchronous counters because it toggles on each clock pulse when its input is held high?

  1. SR latch
  2. D flip-flop
  3. JK flip-flop Correct answer.
  4. Schmitt trigger

Explanation

A JK flip-flop with J and K tied high toggles on every active clock edge, which is the basic action needed in a counter stage. The JK design also avoids the invalid state of a simple SR latch.

Question 13Information, Electronics and Communications Technology (IECT)

In a Class C IPv4 address, which portion identifies the network?

  1. The first 24 bits Correct answer.
  2. The first 8 bits
  3. The first 16 bits
  4. The first 32 bits

Explanation

Class C addresses use a default mask of 255.255.255.0, so the first 24 bits define the network and the last 8 bits identify hosts. This allows 254 usable host addresses per network.

Question 14Information, Electronics and Communications Technology (IECT)

Which protocol translates a domain name such as a website address into an IP address?

  1. DHCP
  2. SNMP
  3. ARP
  4. DNS Correct answer.

Explanation

The Domain Name System resolves human-readable names into IP addresses. ARP maps IP addresses to MAC addresses, which is a different function.

Question 15Information, Electronics and Communications Technology (IECT)

Which transmission medium uses total internal reflection to carry light signals?

  1. Microwave link
  2. Coaxial cable
  3. Optical fibre Correct answer.
  4. Twisted-pair cable

Explanation

Optical fibre confines light in a core with a lower-refractive-index cladding, so light reflects internally along the fibre. This gives very high bandwidth and immunity to electromagnetic interference.

Question 16Information, Electronics and Communications Technology (IECT)

In a 7-bit ASCII code, how many distinct characters can be represented?

  1. 128 Correct answer.
  2. 512
  3. 64
  4. 256

Explanation

With 7 bits there are 2^7 = 128 distinct code combinations. An 8-bit extension would allow 256 combinations.

Question 17Information, Electronics and Communications Technology (IECT)

Which of the following best describes the function of an interrupt in a microprocessor system?

  1. It increases the clock frequency of the processor
  2. It permanently halts the processor until reset
  3. It signals the processor to suspend the current routine and service an event Correct answer.
  4. It stores program code in non-volatile memory

Explanation

An interrupt is a signal that causes the CPU to save its current state, run an interrupt service routine, and then resume the interrupted program. This allows timely handling of external events without polling.

Question 18Information, Electronics and Communications Technology (IECT)

Which modulation technique changes the phase of a carrier wave in proportion to the message signal?

  1. AM
  2. PCM
  3. PSK Correct answer.
  4. FM

Explanation

Phase-shift keying varies the carrier phase to represent digital symbols. Amplitude and frequency remain constant, which helps in noisy channels.

Question 19Information, Electronics and Communications Technology (IECT)

A computer has a 20-bit address bus. What is the maximum directly addressable memory space?

  1. 4 MB
  2. 512 KB
  3. 2 MB
  4. 1 MB Correct answer.

Explanation

Addressable locations equal 2^20 = 1,048,576, which is 1 MB when each location holds one byte. Each additional address line doubles the addressable space.

Question 20Information, Electronics and Communications Technology (IECT)

Which network topology provides redundant paths so that a single cable failure does not disconnect the network?

  1. Ring topology
  2. Bus topology
  3. Star topology
  4. Mesh topology Correct answer.

Explanation

In a full mesh every node connects to every other node, so alternate routes exist when a link fails. This redundancy improves reliability at the cost of more cabling.

Question 21Information, Electronics and Communications Technology (IECT)

What is the result of adding the binary numbers 1011 and 0110?

  1. 11001
  2. 10111
  3. 10001 Correct answer.
  4. 10011

Explanation

1011 is 11 and 0110 is 6, and their sum 17 is 10001 in binary. Column addition gives a carry out of the most significant bit.

Question 22Information, Electronics and Communications Technology (IECT)

A subnet uses the mask 255.255.255.192. How many usable host addresses does it provide?

  1. 126
  2. 64
  3. 30
  4. 62 Correct answer.

Explanation

The mask leaves 6 host bits, giving 2^6 = 64 addresses, of which the network and broadcast addresses are reserved, so 62 are usable. A /27 mask therefore supports 62 hosts.

Question 23Information, Electronics and Communications Technology (IECT)

A signal has a bandwidth of 3 kHz and is sampled at the Nyquist rate, then encoded with 8 bits per sample. What is the resulting bit rate?

  1. 96 kbps
  2. 48 kbps Correct answer.
  3. 12 kbps
  4. 24 kbps

Explanation

The Nyquist rate is twice the highest frequency, so 3 kHz bandwidth requires 6000 samples per second. Multiplying by 8 bits per sample gives 48,000 bits per second, or 48 kbps.

Question 24Information, Electronics and Communications Technology (IECT)

Which statement correctly distinguishes a microprocessor from a microcontroller?

  1. Both contain identical internal blocks and differ only in clock speed
  2. A microprocessor is used only for analog signal processing, while a microcontroller handles digital logic
  3. A microcontroller integrates CPU, memory and peripherals on one chip, while a microprocessor is primarily a CPU requiring external support chips Correct answer.
  4. A microprocessor integrates CPU, memory and peripherals on one chip, while a microcontroller has only a CPU

Explanation

A microcontroller is a complete computer-on-chip with CPU, RAM, ROM and I/O peripherals, suited to embedded control. A general-purpose microprocessor exposes the bus externally and needs separate memory and interface chips.

Question 25Information, Electronics and Communications Technology (IECT)

In a CSMA/CD local area network, what happens when two stations detect a collision during transmission?

  1. The station with the lower MAC address continues transmitting
  2. Both stations stop transmitting and wait a random back-off time before retrying Correct answer.
  3. Both stations immediately retransmit the same frame
  4. The hub assigns a new IP address to each station

Explanation

Collision detection makes stations abort transmission, send a jam signal, and then retry after a random back-off interval to reduce repeated collisions. Randomization prevents the same pair from colliding indefinitely.

Question 26Information, Electronics and Communications Technology (IECT)

Which number system uses the digits 0 through 9 plus the letters A through F, with each position representing a power of sixteen?

  1. Binary
  2. Octal
  3. Binary-coded decimal
  4. Hexadecimal Correct answer.

Explanation

Hexadecimal is base 16, so it needs sixteen symbols: 0-9 supply the first ten and A-F supply values ten to fifteen. Each digit position therefore has a place value that is a power of sixteen. Octal is base 8, binary is base 2 and BCD encodes each decimal digit separately in four bits.

Question 27Information, Electronics and Communications Technology (IECT)

A logic gate produces a HIGH output only when all of its inputs are HIGH. Which gate is it?

  1. XOR gate
  2. OR gate
  3. AND gate Correct answer.
  4. NOR gate

Explanation

The AND function is defined by the rule that the output is 1 only for the input combination in which every input is 1. Any single LOW input forces the output LOW. OR, NOR and XOR all produce a HIGH output for at least one input pattern containing a LOW input.

Question 28Information, Electronics and Communications Technology (IECT)

In the IECT context, which unit is used to express the clock speed of a microprocessor?

  1. Hertz Correct answer.
  2. Ohm
  3. Byte
  4. Volt

Explanation

Clock speed measures how many timing cycles occur per second, so it is expressed in hertz and its multiples such as megahertz and gigahertz. The byte measures storage capacity, while the volt and ohm measure electrical potential and resistance.

Question 29Information, Electronics and Communications Technology (IECT)

Which memory type loses its stored contents when the power supply is removed?

  1. EEPROM
  2. RAM Correct answer.
  3. Flash memory
  4. ROM

Explanation

RAM is volatile: it depends on continuous power to hold charge in its cells and its contents are lost at power-down. ROM, flash and EEPROM are all non-volatile technologies that retain data without power. This volatility is why programs must be reloaded into RAM after each start-up.

Question 30Information, Electronics and Communications Technology (IECT)

Which software category includes operating systems, device drivers and utility programs?

  1. System software Correct answer.
  2. Programming language
  3. Application software
  4. Firmware stored in ROM

Explanation

System software manages the hardware and provides the platform on which other programs run; operating systems, drivers and utilities belong to this category. Application software performs user-oriented tasks such as word processing. A programming language is a notation for writing programs, not a software category of this kind.

Question 31Information, Electronics and Communications Technology (IECT)

In an IPv4 datagram, which field prevents a packet from circulating in a network forever?

  1. Fragment offset
  2. Total length
  3. Time to Live Correct answer.
  4. Header checksum

Explanation

Time to Live is decremented by each router that forwards the datagram, and the datagram is discarded when the value reaches zero. This bounds the lifetime of a packet and prevents endless looping. The checksum protects header integrity, the fragment offset locates a fragment and total length gives the datagram size.

Question 32Information, Electronics and Communications Technology (IECT)

Which of the following is a synchronous serial communication bus commonly used by microcontrollers to interface with sensors and memory chips?

  1. UART
  2. RS-232
  3. I2C Correct answer.
  4. USB

Explanation

I2C is a synchronous two-wire bus in which a clock line times data transfers between a master and addressed slaves, making it popular for on-board sensor and memory connections. UART and RS-232 are asynchronous serial links without a shared clock. USB is a host-based external bus rather than a simple two-wire chip-level interface.

Question 33Information, Electronics and Communications Technology (IECT)

What does the acronym ICT stand for in the context of this examination?

  1. Integrated Circuit Technology
  2. Information and Communication Technology Correct answer.
  3. Instruction Cycle Timing
  4. International Computer Terminal

Explanation

ICT denotes Information and Communication Technology, the field covering computing hardware, software, networking and telecommunications together. The other expansions describe narrower technical concepts such as circuit fabrication or processor timing.

Question 34Information, Electronics and Communications Technology (IECT)

A 4-bit binary counter is reset to 0000. After exactly 13 clock pulses, what is its output?

  1. 1110
  2. 1101 Correct answer.
  3. 1011
  4. 1100

Explanation

Starting from 0000, each pulse increments the count, so after 13 pulses the counter holds the binary value of decimal 13. Decimal 13 equals 8 + 4 + 1, which is 1101 in four bits.

Question 35Information, Electronics and Communications Technology (IECT)

An 8-bit analog-to-digital converter has a full-scale input range of 0 to 5 V. What is the approximate resolution of one least significant bit?

  1. 39.0 mV
  2. 19.5 mV Correct answer.
  3. 2.5 mV
  4. 5.0 mV

Explanation

An 8-bit converter divides the range into 255 steps, so the step size is 5 V divided by 255, which is about 19.6 mV. This step is the smallest input change that produces a new output code.

Question 36Information, Electronics and Communications Technology (IECT)

Which statement correctly describes the difference between a latch and a flip-flop?

  1. A latch is edge-triggered, whereas a flip-flop is level-sensitive.
  2. A flip-flop stores analog values, whereas a latch stores digital values.
  3. A latch is level-sensitive, whereas a flip-flop is edge-triggered. Correct answer.
  4. Both are edge-triggered but a latch has no output.

Explanation

A latch responds to the level of its enable input and is transparent while enabled, whereas a flip-flop captures its input only at a defined clock edge. Edge triggering makes flip-flop behaviour predictable in synchronous designs. Both devices are bistable digital storage elements with outputs.

Question 37Information, Electronics and Communications Technology (IECT)

A signal is band-limited to 4 kHz. What is the minimum sampling rate required to reconstruct it without aliasing?

  1. 16 kHz
  2. 2 kHz
  3. 8 kHz Correct answer.
  4. 4 kHz

Explanation

The Nyquist criterion requires sampling at no less than twice the highest frequency present in the signal. Twice 4 kHz gives 8 kHz, and sampling below this rate would fold high-frequency content into the baseband as aliasing.

Question 38Information, Electronics and Communications Technology (IECT)

Which addressing mode uses an operand value that is contained directly within the instruction itself?

  1. Indexed addressing
  2. Direct addressing
  3. Indirect addressing
  4. Immediate addressing Correct answer.

Explanation

In immediate addressing the operand is embedded in the instruction word, so no memory fetch is needed to obtain it. Direct addressing places a memory address in the instruction, indirect addressing places the address of an address, and indexed addressing adds an index register to a base address.

Question 39Information, Electronics and Communications Technology (IECT)

A 1 kHz square wave is applied to a digital input. What is its period?

  1. 0.5 ms
  2. 1 ms Correct answer.
  3. 10 ms
  4. 0.1 ms

Explanation

Period is the reciprocal of frequency, so 1 divided by 1000 Hz equals 0.001 s, or 1 ms. The period covers one complete cycle including both the high and low portions of the waveform.

Question 40Information, Electronics and Communications Technology (IECT)

In a star topology, what is the principal consequence of a failure of one connecting cable?

  1. The entire network stops working.
  2. The hub automatically reconnects the device through another cable.
  3. All devices slow down but remain connected.
  4. Only the device attached to that cable loses connectivity. Correct answer.

Explanation

In a star topology each device has its own dedicated link to a central hub or switch, so a single cable failure isolates only that device. The remaining links continue to operate normally through the central device.

Question 41Information, Electronics and Communications Technology (IECT)

A host is configured with IP address 192.168.10.130 and mask 255.255.255.192. Which address is the network address of its subnet?

  1. 192.168.10.128 Correct answer.
  2. 192.168.10.192
  3. 192.168.10.0
  4. 192.168.10.64

Explanation

The mask 255.255.255.192 creates blocks of 64 addresses, so the subnets begin at .0, .64, .128 and .192. The host .130 falls in the block starting at .128, which is therefore the network address.

Question 42Information, Electronics and Communications Technology (IECT)

Which protocol operates at the transport layer and provides connectionless, best-effort delivery without acknowledgements?

  1. ARP
  2. TCP
  3. UDP Correct answer.
  4. ICMP

Explanation

UDP is a transport-layer protocol that sends datagrams without establishing a connection or retransmitting lost data, which suits real-time traffic. TCP provides connection-oriented, reliable delivery, while ICMP and ARP operate at the network layer for diagnostics and address resolution.

Question 43Information, Electronics and Communications Technology (IECT)

Which statement about the fetch-decode-execute cycle is correct?

  1. Decoding always requires a memory read cycle.
  2. The program counter holds the instruction currently being executed.
  3. The program counter holds the address of the next instruction to be fetched. Correct answer.
  4. The instruction register holds the address of the next instruction.

Explanation

The program counter stores the address of the next instruction to fetch, and it is incremented as part of the fetch sequence. The fetched instruction itself is placed in the instruction register for decoding. Decoding is performed by control logic and does not itself require a memory access.

Question 44Information, Electronics and Communications Technology (IECT)

A 555 timer is connected as an astable multivibrator. What output behaviour results?

  1. A constant DC level with no variation
  2. A single pulse of fixed width after each trigger
  3. A sinusoidal output at the supply frequency
  4. A continuous rectangular waveform Correct answer.

Explanation

In astable mode the 555 timer repeatedly charges and discharges its timing capacitor, producing a free-running rectangular wave whose frequency and duty cycle are set by external resistors and a capacitor. Monostable mode, by contrast, gives one pulse per trigger.

Question 45Information, Electronics and Communications Technology (IECT)

An amplifier has a voltage gain of 100. What is this gain in decibels?

  1. 100 dB
  2. 20 dB
  3. 40 dB Correct answer.
  4. 10 dB

Explanation

Voltage gain in decibels is 20 times the base-10 logarithm of the ratio. The logarithm of 100 is 2, and 20 times 2 equals 40 dB. Using 10 times the logarithm would apply to power ratios, not voltage ratios.

Question 46Information, Electronics and Communications Technology (IECT)

Two 8-bit numbers are added in an arithmetic logic unit and the carry out of the most significant bit is 1 while the sign bit of the result is 0. Which condition does this indicate for signed two's complement operands?

  1. An overflow has occurred Correct answer.
  2. The operands must both be positive
  3. The result is always zero
  4. No overflow has occurred

Explanation

In two's complement addition, overflow occurs when the carry into the sign bit differs from the carry out of the sign bit. Here the carry out is 1 and the resulting sign bit is 0, so the carries differ and signed overflow is flagged.

Question 47Information, Electronics and Communications Technology (IECT)

An instruction pipeline has five stages and each stage takes one clock cycle. With no hazards, how many clock cycles are needed to complete four independent instructions?

  1. 4 cycles
  2. 20 cycles
  3. 8 cycles Correct answer.
  4. 5 cycles

Explanation

The first instruction needs five cycles to fill the pipeline, and each of the remaining three instructions completes one cycle later, giving 5 + 3 = 8 cycles. The non-pipelined time would be 4 times 5 = 20 cycles, so pipelining nearly halves the time here.

Question 48Information, Electronics and Communications Technology (IECT)

A 16-bit CPU uses a 20-bit address bus with memory organised in 16-bit words. What is the maximum number of words it can address?

  1. 2^16 words
  2. 2^36 words
  3. 2^20 words Correct answer.
  4. 2^4 words

Explanation

The address bus width determines the number of addressable locations, so 20 address lines give 2^20 distinct addresses. The data width of 16 bits affects word size, not the number of addressable words. The 16-bit CPU designation refers to data and register width.

Question 49Information, Electronics and Communications Technology (IECT)

In a network using classless inter-domain routing, an organisation is allocated the block 200.10.4.0/22. Which address lies outside this block?

  1. 200.10.6.200 Correct answer.
  2. 200.10.5.10
  3. 200.10.4.255
  4. 200.10.7.254

Explanation

A /22 prefix fixes the first 22 bits, leaving the last 10 bits variable, so the block spans 200.10.4.0 to 200.10.7.255. Every address from .4.0 through .7.255 belongs to it, and 200.10.6.200 does lie inside that range, so it is not the outside address.

Question 50Information, Electronics and Communications Technology (IECT)

A source encoder removes statistical redundancy from a data stream. Which statement best explains the resulting effect on transmission?

  1. The signal bandwidth is increased to improve noise immunity.
  2. The average number of bits per symbol is reduced while the information content is preserved. Correct answer.
  3. The data is encrypted so that only the receiver can decode it.
  4. The bit rate is increased so that the channel is used more fully.

Explanation

Source coding assigns shorter codes to more probable symbols, lowering the average bits per symbol without losing information, which is the essence of data compression. Encryption for secrecy is a separate function, and channel coding adds redundancy rather than removing it.