CS MCQs

Logic Gates MCQs, Set 1 of 1

Q1 / 16

  1. Q1. Which gate outputs 1 only when all its inputs are 1?

    • A.OR
    • B.AND(correct answer)
    • C.XOR
    • D.NOR

    AND is true only when every input is true.

  2. Q2. Which gate outputs 1 when at least one input is 1?

    • A.AND
    • B.NAND
    • C.OR(correct answer)
    • D.XNOR

    OR is true if any input is true.

  3. Q3. Which gate outputs 1 when its two inputs are different?

    • A.XOR(correct answer)
    • B.XNOR
    • C.AND
    • D.NOR

    XOR (exclusive OR) is true when exactly one input is true.

  4. Q4. What is the output of a NAND gate when both inputs are 1?

    • A.0(correct answer)
    • B.1
    • C.Undefined
    • D.Same as input A

    AND gives 1, and NAND inverts it to 0.

  5. Q5. What is the output of a NOR gate when both inputs are 0?

    • A.0
    • B.1(correct answer)
    • C.Undefined
    • D.Same as input B

    OR gives 0, and NOR inverts it to 1.

  6. Q6. Which gates are called universal gates?

    • A.AND and OR
    • B.NAND and NOR(correct answer)
    • C.XOR and XNOR
    • D.NOT and AND

    Any logic circuit can be built from only NAND gates, or only NOR gates.

  7. Q7. A NOT gate is also called an:

    • A.Buffer
    • B.Inverter(correct answer)
    • C.Amplifier
    • D.Encoder

    It inverts its input: 0 becomes 1 and 1 becomes 0.

  8. Q8. By De Morgan’s law, NOT (A AND B) equals:

    • A.NOT A AND NOT B
    • B.NOT A OR NOT B(correct answer)
    • C.A OR B
    • D.A AND B

    Negating an AND turns it into an OR of the negated inputs.

  9. Q9. How many rows are in the truth table of a function with 3 inputs?

    • A.3
    • B.6
    • C.8(correct answer)
    • D.9

    2³ = 8 input combinations.

  10. Q10. What is A XOR A?

    • A.0(correct answer)
    • B.1
    • C.A
    • D.NOT A

    Both inputs are always the same, so XOR gives 0.

  11. Q11. What is A OR 1 in Boolean algebra?

    • A.A
    • B.0
    • C.1(correct answer)
    • D.NOT A

    Anything OR true is true.

  12. Q12. What is A AND 0 in Boolean algebra?

    • A.0(correct answer)
    • B.1
    • C.A
    • D.NOT A

    Anything AND false is false.

  13. Q13. A half adder produces which two outputs?

    • A.Sum and Carry(correct answer)
    • B.Sum and Borrow
    • C.Difference and Carry
    • D.Quotient and Remainder

    It adds two bits, giving a sum bit and a carry bit.

  14. Q14. In a half adder, the Sum output comes from which gate?

    • A.AND
    • B.OR
    • C.XOR(correct answer)
    • D.NAND

    Sum = A XOR B; Carry = A AND B.

  15. Q15. Which circuit selects one of several inputs and sends it to a single output?

    • A.Decoder
    • B.Multiplexer(correct answer)
    • C.Demultiplexer
    • D.Encoder

    A multiplexer (MUX) uses select lines to choose one input.

  16. Q16. How many bits does a single flip-flop store?

    • A.1(correct answer)
    • B.2
    • C.4
    • D.8

    A flip-flop is a 1-bit memory element.

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