Question

The logic gates in which all the inputs must be low to get a high output are:

• A. NAND and AND
• B. NOR and NAND
• C. OR and AND
• D. AND and NOR

Hint:

A NOR gate is called a universal gate and produces a high output only when all inputs are low.

Answer 1

The Correct Option is B

Step 1: Understand the NOR gate.
A NOR gate gives high output only when all inputs are low.
For two inputs: \[ A=0,\quad B=0 \] then \[ Y=1 \] For any other combination, \[ Y=0 \] Thus, NOR gate satisfies the condition.

Step 2: Understand the NAND gate.
A NAND gate gives low output only when all inputs are high.
Therefore, if all inputs are low, the output becomes high.
For example: \[ A=0,\quad B=0 \] then \[ Y=1 \] Hence, NAND gate also gives high output when all inputs are low.

Step 3: Analyze the remaining gates.

AND gate:
AND gate gives high output only when all inputs are high. Hence, it does not satisfy the condition.

OR gate:
OR gate gives high output even if one input is high. Hence, it does not satisfy the condition.

Step 4: Final conclusion.
Therefore, the required logic gates are \[ \boxed{\text{NOR and NAND}} \] Hence, the correct option is \[ \boxed{(2)} \]