# 49+ Critical Digital Electronics MCQs and Answers for Competitive exams

## 1. What is the number of outputs of a full adder circuit?

1) Two

2) Three

3) Four

4) One

Solution: 2) Three

## 2. What is the expression for the sum(s) of a half adder if the inputs are A & B?

1) S = A OR B

2) S = A AND B

3) S = A XNOR B

4) S = A XOR B

Solution: 4) A XOR B

Critical Electronics MCQ Series

## 3. What is the sum(S) expression of a full adder if the inputs are A, B & C?

1) S = A OR B AND C

2) S = A AND B OR C

3) S = A XNOR B XOR C

4) S = A XOR B XOR C

Solution: 4) A XOR B XOR C

## 10101 + 1011

Do you know how to perform binary addition in digital electronics? Click to know!

1) 1 0 0 0 0

2) 1 0 1 0 1 0

3) 1 0 0 0 0 0

4) 1 1 1 1 0 0

Solution: 3) 1 0 0 0 0 0

## 5. Which of these following logic gates gives a high output when both the inputs are low?

1) NOR gate

2) NOT gate

3) NAND gate

4) ALL OF THE ABOVE

Solution: 4) ALL OF THE ABOVE

## 6. Which of these following does not include in an ALU (Arithmetic Logic Unit)?

4) None of the above

Solution: 3) Multiplexer

1) XOR

2) NAND

3) NOR

4) NOT

Solution: 1) XOR

## 8. How many bits does the sum of the full adder consists of?

1) Four bits

2) Three bits

3) Two bits

4) Five bits

Solution: 3) Two bits

## 9. A combinational circuit calculates the arithmetic sum in a parallel way. What is the name of the adder?

4) Both 1) & 2)

Solution: 2) Parallel Adder

## 10. What is the primary object that is needed for VLSI technology?

1)  NOR gate

2) NAND gate

3) Both 1) and 2)

4) Gate array

Solution: 4) Gate array.

## Statement: A binary subtractor can be made using a binary adder.

1. True
2. False

Solution: (1). True

How binary adders can make binary subtractors! Click to know!

## 12. A circuit takes single input but provides multiple outputs. Identify which circuit it could be.

1) Multiplexer

2) Demultiplexer

3) Encoder

4) All of them

Solution: 2) Demultiplexer

## 13. What does a multiplexer do?

1) It takes multiple inputs and provides a single output.

2) It takes a single output and offers multiple outputs.

3) It inverts the input.

4) None of the above.

Solution: 1) It takes multiple inputs and provides a single output.

1) One

2) Four

3) Three

4) Two

Solution: 4) Two

## Statement:An Encoder can be used as a transducer.

1. True
2. False

Solution: (1). True

## 16. How does a priority set?

1) The lower the subscript number, the higher the priority.

2) The higher the subscript number, the lower the priority.

3) The higher the subscript number, the higher the priority.

4) None of the above.

Solution: 3) The higher the subscript number, the higher the priority.

## 0110 + 0101

1) 10001

2) 11001

3) 1011

4) 1111

Solution: 1) 10001

What is BCD Adder? Know Here!

## 1101 – 1011

Do you know how to perform binary subtraction in digital electronics? Click to know!

1) 10001

2) 0010

3) 1011

4) 0001

Solution: 2) 0010

## Statement:The logical expression for both the full adders and full subtractors are the same.

1. True
2. False

Solution: (1). True

## 20. Which type of complement method is used for the decimal number system?

1) 10’s compliment

2) 8’s compliment

3) 9’s compliment

4) Both 1) and 3)

Solution: 4) Both 1) and 3)

## 21. How many select lines will be there if the inputs of a MUX are 8?

1) One

2) Four

3) Three

4) Five

Solution: 3) Three

1) One

2) Five

3) Three

4) Two

Solution: 1) Two

## 23. Recording a video clip is which type of operation?

1) Multiplexing

2) De Multiplexing

3) Encoding

4) Decoding

Solution: 3) Encoding

1) One

2) Two

3) Three

4) Four

Solution: 1) One

## Statement:Multiplexers cannot implement Boolean functions.

1. True
2. False

Solution: (2). False

## 26. Which circuit can perform the increment operation of an ALU?

2) Subtractor

3) Both 1) and 2)

4) None of them

Solution: 3) Both 1) and 2)

## Statement:Technologies like TDM, FDM, CDMA, etc., uses multiplexers and demultiplexers.

1. True
2. False

Solution: (1). True

1) n

2) 2n

3) 2n – 1

4) n-1

Solution: 1) n

## 29. Which type of basic gates is most necessary for Encoders?

1) OR gates

2) AND gates

3) NOT gates

4) All of the above

Solution: 1) OR gates

## Statement:DTMF is Diode Time Multiplexer Frequency.

1. True
2. False

Solution: (2). False. DTMF – DUAL TONE MULTIPLE FREQUENCY.

## 31. What is the lowest number of NAND gates required for a half subtractors?

1) Four

2) Five

3) Six

4) Seven

Solution: 2) Five

## 32. A decoder has four input lines. How many output lines will be there?

1) Eight

2) One

3) Four

4) Sixteen

Solution: 4) Sixteen

## Statement:An encoder takes multiple data inputs and converts them into a single output with select lines.

1. True
2. False

Solution: (2). False

## 34. What is min-term?

1) Product of sum

2) Sum of product

3) Product of product

4) Sum of the sum

Solution: 1) Product of sum

## 35. Find the application of a MUX.

1) It is used in Analog to Digital converters and Digital to analog converters in digital electronics.

2) It is used in rectifiers.

3) It is used in filters.

4) None of the above is correct.

Solution: 1) It is used in Analog to Digital converters and Digital to analog converters in digital electronics.

## Statement: An operation in Flip Flop is faster than an operation in the multiplexer.

1. True
2. False

Solution: (2). False

## 37. Which IC works as a multiplexer?

1) 74HA198

2) 74HC150

3) 74CH199

4) 74HC157

Solution: 4) 74HC157

## 38. Which IC works as a demultiplexer?

1) 74HC83

2) 74HC38

3) 74CH19

4) 74HC15

Solution: 1) 74HC83

## 39. Which IC works as Encoder?

1) HT85A

2) HT87B

3) HT12E

4) HT74F

Solution: 3) HT12E

1) 1

2) 2

3) 4

4) 5

Solution: 1) 1

1) 1

2) 2

3) 4

4) 5

Solution: 2) 2

1) 1

2) 2

3) 3

4) 4

Solution: 1) 1

1) 1

2) 2

3) 3

4) 4

Solution: 2) 2

## 44. Which gates are known as universal gates in digital electronics ?

1) OR and AND

2) NOT and XOR

3) NOR and NAND

4) All of them

Solution: 3) NOR and NAND

## 45. A truth table is given below where A and B are the provided inputs, and from Y the output is taken. Identify the Logic gate.

1) XOR

2) NAND

3) XNOR

4) NOR

Solution: 3) XNOR

1) XOR

2) NAND

3) XNOR

4) NOR

Solution: 4) NOR

## 47. Find the odd one out from the digital electronics circuitry.

1) MULTIPLEXER

3) REGISTERS

4) COUNTERS

Solution: 1) MULTIPLEXER

## 48. What is the lowest no. of NOT gate required for the given expression?

Y = A’B + B’C + AC

1) 1

2) 2

3) 3

4) 4

Solution: 1) 1

## 49. Find the odd one out.

1) DEMULTIPLEXERS

2) ENCODERS

4) FULL SUBTRACTORS

Solution: 1) DEMULTIPLEXERS

## 50. A truth table is given below where A and B are the provided inputs, and from Y the output is taken, for a digital electronics circuitry. Identify the combinational circuit.

4) Both 1) and 3)

Solution: 4) Both 1) and 3)