1. What is the binary equivalent of the decimal number 25?

A. 11001
B. 10101
C. 10011
D. 11100
Answer: A. 11001
Explanation:
25 divided by 2 repeatedly gives remainders:
25 ÷ 2 = 12, remainder 1
12 ÷ 2 = 6, remainder 0
6 ÷ 2 = 3, remainder 0
3 ÷ 2 = 1, remainder 1
1 ÷ 2 = 0, remainder 1
So, in reverse: 11001
2. The logic gate which gives a HIGH output when any one of its input is HIGH is:
A. AND
B. OR
C. NOT
D. NAND
Answer: B. OR
Explanation:
An OR gate outputs HIGH (1) if any one or more inputs are HIGH.
3. Which logic gate is known as the universal gate?
A. AND
B. OR
C. NOR
D. NAND
Answer: D. NAND
Explanation:
NAND gates can be used to create all basic logic gates (AND, OR, NOT), making
them universal.
4. The two's complement of binary number 0101 is:
A. 1010
B. 1101
C. 1011
D. 1111
Answer: C. 1011
Explanation:
Invert 0101 → 1010
Add 1 → 1011
5. A half adder adds:
A. Two binary digits
B. Three binary digits
C. Four binary digits
D. Only decimal numbers
Answer: A. Two binary digits
Explanation:
A half adder adds two single-bit binary numbers and gives sum and carry outputs.
6. The function of a multiplexer is:
A. To perform arithmetic operations
B. To decode binary inputs
C. To select one of many inputs and pass it to output
D. To store data temporarily
Answer: C. To select one of many inputs and pass it to output
Explanation:
A multiplexer (MUX) selects one input from many using select lines and forwards it to
the output.
7. What is the output of a NOT gate if the input is 1?
A. 1
B. 0
C. Undefined
D. High impedance
Answer: B. 0
Explanation:
A NOT gate inverts the input. So, NOT 1 = 0.
8. The Boolean expression for a NAND gate is:
A. A + B
B. A·B
C. (A·B)'
D. (A + B)'
Answer: C. (A·B)'
Explanation:
NAND gate performs AND followed by NOT. So, output = NOT (A AND B) = (A·B)'
9. What is the number of combinations for a 4-input truth table?
A. 8
B. 16
C. 10
D. 32
Answer: B. 16
Explanation:
Number of combinations = 2ⁿ
Here, n = 4 → 2⁴ = 16
10. A full adder can be made using:
A. 2 XOR gates
B. 2 Half adders and an OR gate
C. 1 Half adder and 1 AND gate
D. 3 Half adders
Answer: B. 2 Half adders and an OR gate
Explanation:
Full Adder = Half Adder for A, B → Sum1, Carry1;
Then Sum1 + Cin using another half adder → Final Sum, Carry2;
Carry1 OR Carry2 = Final Carry.
11. A decoder converts:
A. Binary to Gray code
B. Binary to Decimal
C. n-input binary code to 2ⁿ unique outputs
D. Decimal to Binary
Answer: C. n-input binary code to 2ⁿ unique outputs
Explanation:
A decoder takes an n-bit input and activates only one of the 2ⁿ outputs.
12. A flip-flop is used for:
A. Arithmetic operations
B. Data transmission
C. Data storage
D. Signal amplification
Answer: C. Data storage
Explanation:
Flip-flops are basic memory elements that store 1-bit of information.
13. In positive logic, logic 1 is represented by:
A. 0V
B. -5V
C. +5V
D. +3.3V
Answer: C. +5V
Explanation:
In positive logic, a higher voltage level (e.g., +5V) represents logic 1.
14. A D flip-flop:
A. Has two inputs
B. Transfers input D to output Q on the clock edge
C. Acts as a decoder
D. Is not edge-triggered
Answer: B. Transfers input D to output Q on the clock edge
Explanation:
D flip-flop: “Data” or “Delay” flip-flop — it latches input D at the clock edge.
15. Which one is NOT a type of flip-flop?
A. SR
B. JK
C. D
D. FX
Answer: D. FX
Explanation:
There is no flip-flop called FX. Common types: SR, JK, D, T.
16. A binary counter counts:
A. From 0 to 10
B. In binary numbers
C. In decimal only
D. Odd numbers
Answer: B. In binary numbers
Explanation:
Binary counters count sequentially in binary format (e.g., 000, 001, 010...).
17. Gray code is used in:
A. Error correction
B. Digital communication
C. Shaft encoders
D. Floating-point arithmetic
Answer: C. Shaft encoders
Explanation:
Gray code changes only one bit between successive values, ideal for mechanical
encoders.
18. What is the binary equivalent of hexadecimal number A2?
A. 10100010
B. 11000010
C. 10110010
D. 10010010
Answer: A. 10100010
Explanation:
A = 1010, 2 = 0010 → A2 = 10100010 in binary
19. What is the output of a XOR gate with both inputs 1?
A. 0
B. 1
C. Undefined
D. High
Answer: A. 0
Explanation:

XOR gate gives 1 only when inputs are different. Here, 1 ⊕ 1 = 0

20. In a 3-bit counter, the maximum count is:
A. 3
B. 7
C. 6
D. 8
Answer: B. 7
Explanation:
3 bits → Max binary: 111 → Decimal = 7
41. What is the purpose of the enable input in logic circuits like multiplexers and
decoders?
A. To increase power
B. To allow or block the function of the circuit
C. To add delay
D. To reduce size
Answer: B. To allow or block the function of the circuit
Explanation:
Enable input controls whether the circuit operates or stays inactive.
42. A ring counter is formed using:
A. Multiplexers
B. Shift registers
C. Decoders
D. Flip-flops in parallel
Answer: B. Shift registers
Explanation:
A ring counter is a circular shift register where the output of the last flip-flop is fed to
the first.
43. The 1's complement of binary number 101100 is:
A. 010011
B. 110011
C. 011011
D. 010100
Answer: A. 010011
Explanation:
1's complement is found by inverting each bit:
1 → 0, 0 → 1 → 101100 → 010011
44. Which number system uses only digits 0 and 1?
A. Octal
B. Hexadecimal
C. Binary
D. Decimal
Answer: C. Binary
Explanation:
Binary uses only two digits: 0 and 1.
45. Which flip-flop is also called a toggle flip-flop?
A. D flip-flop
B. SR flip-flop
C. JK flip-flop
D. T flip-flop
Answer: D. T flip-flop
Explanation:
T flip-flop toggles the output on every clock pulse when T = 1.
46. Which of the following circuits converts serial data to parallel data?
A. Multiplexer
B. Demultiplexer
C. Serial-in Parallel-out shift register
D. Encoder
Answer: C. Serial-in Parallel-out shift register
Explanation:
This type of shift register accepts serial input and provides parallel output.
47. Which of these is not a number system?
A. Decimal
B. Binary
C. Ternary
D. Logical
Answer: D. Logical
Explanation:
Logical is not a number system; it’s a concept used in digital circuits.
48. The carry output of a full adder is 1 only if:
A. Only one input is 1
B. At least two inputs are 1
C. All inputs are 0
D. All inputs are 1
Answer: B. At least two inputs are 1
Explanation:
A full adder adds A, B, and Cin. Carry = 1 if two or more inputs are 1.
49. What is the binary value of (5 + 3)?
A. 1001
B. 1000
C. 1100
D. 0101
Answer: A. 1000
Explanation:
5 + 3 = 8 → Binary of 8 = 1000
50. In a 3-to-8 decoder, how many output lines are there?
A. 3
B. 6
C. 8
D. 9
Answer: C. 8
Explanation:
A decoder with 3 inputs gives 2³ = 8 output lines.
51. Which logic family is the fastest?
A. CMOS
B. TTL
C. ECL
D. RTL
Answer: C. ECL (Emitter-Coupled Logic)
Explanation:
ECL is very fast, due to non-saturating transistors, but consumes more power.
52. Which gate is used in parity checking?
A. AND
B. XOR
C. OR
D. NAND
Answer: B. XOR
Explanation:
XOR gates detect odd parity, useful in error detection.
53. The hexadecimal number F represents decimal:
A. 10
B. 11
C. 14
D. 15
Answer: D. 15
Explanation:
In hexadecimal: A = 10, B = 11, ..., F = 15
54. How many flip-flops are required for a MOD-16 counter?
A. 2
B. 4
C. 5
D. 8
Answer: B. 4
Explanation:
MOD-16 means 16 states → 2⁴ = 16 → 4 flip-flops needed.
55. The truth table of a NAND gate is the opposite of:
A. AND gate
B. OR gate
C. XOR gate
D. NOT gate
Answer: A. AND gate
Explanation:
NAND = NOT of AND → Outputs are opposite of AND gate.
56. In binary subtraction, what is 1011 – 0110?
A. 1001
B. 0101
C. 1111
D. 0011
Answer: B. 0101
Explanation:
Binary of 1011 = 11
0110 = 6
11 – 6 = 5 → Binary = 0101
57. Which of the following is a non-weighted code?
A. BCD
B. Decimal
C. Gray
D. Binary
Answer: C. Gray
Explanation:
Gray code is non-weighted; each bit doesn't represent a specific weight.
58. The circuit which converts analog to digital is called:
A. DAC
B. ADC
C. Modulator
D. Demodulator
Answer: B. ADC (Analog-to-Digital Converter)
Explanation:
An ADC converts analog input signals to digital output.
59. A 3-bit up counter counts from:
A. 000 to 111
B. 001 to 110
C. 111 to 000
D. 100 to 111
Answer: A. 000 to 111
Explanation:
3-bit counter → 2³ = 8 states → Counts from 0 (000) to 7 (111).
60. What is the result of 1101 + 0110?
A. 10111
B. 10011
C. 11111
D. 11011
Answer: A. 10111
Explanation:
1101 = 13
0110 = 6
13 + 6 = 19 → Binary = 10011
61. What does a half adder do?
A. Subtracts two bits
B. Adds three bits
C. Adds two bits and gives sum and carry
D. Only stores data
Answer: C. Adds two bits and gives sum and carry
Explanation:
A half adder adds two single-bit binary numbers and outputs sum and carry.
62. Which of the following is not a combinational circuit?
A. Multiplexer
B. Decoder
C. Counter
D. Full adder
Answer: C. Counter
Explanation:
A counter is a sequential circuit; its output depends on past states.
63. A logic gate that outputs LOW only when all inputs are HIGH is:
A. OR
B. NAND
C. NOR
D. AND
Answer: B. NAND
Explanation:
NAND = NOT + AND → Outputs LOW only when all inputs are HIGH.
64. The Gray code equivalent of binary 1010 is:
A. 1111
B. 1110
C. 1011
D. 1001
Answer: B. 1110
Explanation:
To convert to Gray code:
MSB remains same, next bits are XOR of current and previous →
Binary 1010 → Gray = 1110
65. What is the decimal value of the binary number 11010?
A. 22
B. 24
C. 26
D. 18
Answer: A. 26
Explanation:
11010 = (1×16) + (1×8) + (0×4) + (1×2) + (0×1) = 26
66. In a JK flip-flop, if J=1 and K=0, then output will:
A. Toggle
B. Reset
C. Set
D. Remain unchanged
Answer: C. Set
Explanation:
J = 1, K = 0 → JK flip-flop goes to Set state (Q = 1)
67. The NOT gate is also known as:
A. Buffer
B. Inverter
C. Amplifier
D. Selector
Answer: B. Inverter
Explanation:
NOT gate inverts the input → 1 becomes 0, 0 becomes 1 → Inverter
68. Which logic gate has the truth table: 0, 1, 1, 1?
A. AND
B. OR
C. NOR
D. NAND
Answer: B. OR
Explanation:
OR gate gives 0 only when both inputs are 0, rest are 1 → Truth table: 0,1,1,1
69. In Boolean algebra, A + A = ?
A. 1
B. 0
C. A
D. A'
Answer: C. A
Explanation:
A + A = A (Idempotent Law in Boolean algebra)
70. Which type of counter counts up and down?
A. Ripple counter
B. Ring counter
C. Up-down counter
D. Synchronous counter
Answer: C. Up-down counter
Explanation:
Up-down counter counts both incrementing and decrementing sequences.
71. A multiplexer can be used to implement:
A. Subtractor
B. Comparator
C. Any Boolean function
D. Clock generator
Answer: C. Any Boolean function
Explanation:
A MUX with the right configuration can be used to build any Boolean function.
72. Which logic family is most power-efficient?
A. TTL
B. ECL
C. CMOS
D. RTL
Answer: C. CMOS
Explanation:
CMOS consumes very low power, especially in static conditions.
73. An SR flip-flop has S=0, R=1. Output will be:
A. Set
B. Reset
C. Toggle
D. Hold
Answer: B. Reset
Explanation:
S=0, R=1 → Flip-flop output is Reset (Q = 0)
74. How many combinations are possible with 4 binary inputs?
A. 8
B. 12
C. 16
D. 32
Answer: C. 16
Explanation:
Each input has 2 options → 2⁴ = 16 combinations
75. Which of the following is a memory element?
A. MUX
B. Decoder
C. Flip-Flop
D. Adder
Answer: C. Flip-Flop
Explanation:
Flip-flops store 1-bit data, making them the basic memory elements.
76. What is the output of XOR when A = 1 and B = 1?
A. 1
B. 0
C. A
D. B
Answer: B. 0
Explanation:
XOR outputs 1 if inputs differ, else 0. So, 1 XOR 1 = 0
77. A decoder converts:
A. Decimal to Binary
B. Binary to Decimal
C. Binary to one-hot code
D. ASCII to Binary
Answer: C. Binary to one-hot code
Explanation:
Decoder activates one out of many outputs for each binary input.
78. The output of an SR flip-flop with S = 0 and R = 0 is:
A. Set
B. Reset
C. Toggle
D. No change
Answer: D. No change
Explanation:
S = R = 0 → Flip-flop holds previous state
79. What is the function of a demultiplexer?
A. Many to one
B. One to many
C. Parallel to serial
D. Serial to parallel
Answer: B. One to many
Explanation:
DEMUX takes one input and routes it to one of many outputs
80. Binary of decimal number 12 is:
A. 1001
B. 1100
C. 1110
D. 1010
Answer: B. 1100
Explanation:
12 in binary = (8 + 4 + 0 + 0) = 1100
81. What does ASCII stand for?
A. American Standard Code for Information Interchange
B. Advanced Serial Communication Interface Index
C. Analog Signal Code for Internet Interface
D. Automated Standard Computer Input Interchange
Answer: A. American Standard Code for Information Interchange
Explanation:
ASCII is a 7-bit code used to represent text characters digitally.
82. The main difference between latch and flip-flop is:
A. Latch is faster
B. Flip-flop is level-triggered
C. Latch is edge-triggered
D. Flip-flop is edge-triggered
Answer: D. Flip-flop is edge-triggered
Explanation:
Latches are level-triggered; flip-flops are edge-triggered devices.
83. Which counter does not skip any state?
A. Ripple counter
B. Asynchronous counter
C. Ring counter
D. Synchronous counter
Answer: D. Synchronous counter
Explanation:
Synchronous counters change all flip-flops simultaneously, avoiding skipped states.
84. The function of a parity bit is:
A. Increase memory
B. Error detection
C. Reduce power
D. Encode ASCII
Answer: B. Error detection
Explanation:
Parity bits are added to detect single-bit transmission errors.
85. What is the modulus of a 3-bit binary counter?
A. 3
B. 8
C. 6
D. 7
Answer: B. 8
Explanation:
3 bits → 2³ = 8 states → Mod-8 counter.
86. What is the hexadecimal equivalent of binary 111101?
A. 3F
B. 1E
C. 3D
D. 2F
Answer: C. 3D
Explanation:
Binary 111101 → group as 0011 1101 → Hex = 3D
87. Which of the following is an example of volatile memory?
A. ROM
B. PROM
C. RAM
D. EEPROM
Answer: C. RAM
Explanation:
RAM loses data when power is off, so it is volatile.
88. The Boolean expression A·1 simplifies to:
A. A
B. 0
C. 1
D. A'
Answer: A. A
Explanation:
A AND 1 = A (Identity Law)
89. A 4-to-1 multiplexer has how many selection lines?
A. 4
B. 2
C. 3
D. 1
Answer: B. 2
Explanation:
2 selection lines can select 2² = 4 inputs
90. How many states does a MOD-10 counter have?
A. 8
B. 10
C. 12
D. 4
Answer: B. 10
Explanation:
MOD-10 → Counter counts from 0 to 9 = 10 states
91. What does BCD stand for?
A. Binary Code Direct
B. Bit Coded Decimal
C. Binary Coded Decimal
D. Binary Count Decoder
Answer: C. Binary Coded Decimal
Explanation:
BCD represents each decimal digit separately in binary form.
92. A device that amplifies digital signals is:
A. Flip-flop
B. Buffer
C. MUX
D. Decoder
Answer: B. Buffer
Explanation:
A buffer strengthens the signal without altering its logic value.
93. Decimal number 255 in binary is:
A. 11111111
B. 10101010
C. 11110000
D. 11001100
Answer: A. 11111111
Explanation:
255 = 2⁸ - 1 → All 8 bits are 1 → 11111111
94. A 2-input NOR gate is equivalent to:
A. AND followed by NOT
B. OR followed by NOT
C. XOR followed by NOT
D. NAND followed by NOT
Answer: B. OR followed by NOT
Explanation:
NOR = NOT + OR → Inverts the OR output.
95. Which of these gates is considered a universal gate?
A. OR
B. AND
C. NAND
D. XOR
Answer: C. NAND
Explanation:
NAND and NOR are universal gates — any circuit can be built using only them.
96. Which of the following is not a sequential circuit?
A. Flip-Flop
B. Counter
C. Multiplexer
D. Shift Register
Answer: C. Multiplexer
Explanation:
MUX is a combinational circuit; others are sequential (store state).
97. Which logic gate has a HIGH output only when inputs differ?
A. AND
B. OR
C. XOR
D. NAND
Answer: C. XOR
Explanation:
XOR = Exclusive-OR → Outputs 1 only when inputs are different
98. How many output lines does a 4-to-16 decoder have?
A. 4
B. 8
C. 12
D. 16
Answer: D. 16
Explanation:
Decoder with 4 inputs → 2⁴ = 16 outputs
99. A positive edge-triggered flip-flop responds to:
A. Low to High transition
B. High to Low transition
C. Constant High
D. Constant Low
Answer: A. Low to High transition
Explanation:
Positive edge-triggered means flip-flop triggers on rising clock edge
100. The function of an encoder is:
A. Select one input
B. Convert binary to decimal
C. Convert information to coded format
D. Multiply signals
Answer: C. Convert information to coded format
Explanation:
An encoder converts multiple input lines into a binary code