Digital Electronics – MCQs

By: Prof. Dr. Fazal Rehman | Last updated: May 2, 2025

1. : Which logic gate gives a high output only when all inputs are high?
(A) OR
(B) AND
(C) NAND
(D) NOR

2. : What is the binary equivalent of the decimal number 13?
(A) 1011
(B) 1101
(C) 1110
(D) 1001

3. : Which number system has base 16?
(A) Binary
(B) Octal
(C) Decimal
(D) Hexadecimal

4. : A flip-flop is used to store:
(A) A single bit
(B) A byte
(C) A nibble
(D) A word

5. : Which of the following is a universal gate?
(A) AND
(B) OR
(C) XOR
(D) NAND

6. : The output of a NOR gate is high only when:
(A) All inputs are high
(B) All inputs are low
(C) One input is high
(D) One input is low

7. : What is the full form of TTL?
(A) Time-To-Latch
(B) Transistor-Transistor Logic
(C) Transfer Timing Logic
(D) Tri-state Transistor Logic

8. : What is the minimum number of bits required to represent 256 different values?
(A) 7
(B) 8
(C) 9
(D) 10

9. : A multiplexer is used to:
(A) Add binary numbers
(B) Select one input from many
(C) Convert analog to digital
(D) Encode binary data

10. : The function of an encoder is to:
(A) Decode binary data
(B) Convert binary to analog
(C) Convert multiple inputs to coded output
(D) Count pulses

11. : In a 4-to-16 decoder, how many output lines are there?
(A) 4
(B) 8
(C) 16
(D) 32

12. : What does a D flip-flop do?
(A) Toggles output
(B) Delays the input
(C) Captures input at clock edge
(D) Shifts bits

13. : In Boolean algebra, the identity element for OR operation is:
(A) 0
(B) 1
(C) X
(D) None

14. : A full adder adds:
(A) Two bits
(B) Three bits
(C) Four bits
(D) Eight bits

15. : Which of the following is not a combinational circuit?
(A) Multiplexer
(B) Decoder
(C) Counter
(D) Adder

16. : The output of a NOT gate is:
(A) Always high
(B) Same as input
(C) Inverted input
(D) Always low

17. : What is the output of XOR gate when both inputs are the same?
(A) 0
(B) 1
(C) High impedance
(D) Undefined

18. : Which flip-flop is known as a toggle flip-flop?
(A) D
(B) T
(C) JK
(D) SR

19. : How many combinations are possible with 3 input bits?
(A) 4
(B) 6
(C) 8
(D) 10

20. : Which device stores data in binary form permanently?
(A) RAM
(B) ROM
(C) Flip-Flop
(D) Register

21. : What is the basic building block of a digital circuit?
(A) Microprocessor
(B) Logic gates
(C) Resistors
(D) Transistors

22. : Which logic family has the fastest speed?
(A) TTL
(B) CMOS
(C) ECL
(D) DTL

23. : The propagation delay of a gate is the time taken for:
(A) Output to appear
(B) Signal to travel
(C) Output to change after input changes
(D) Clock signal to arrive

24. : A register is used to:
(A) Perform calculations
(B) Store multiple bits
(C) Decode signals
(D) Transfer analog signals

25. : What is the output of a NAND gate if both inputs are 1?
(A) 0
(B) 1
(C) High impedance
(D) Undefined