Which logic gate given in the options is correct whose output is LOW, if and only if all...
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Which logic gate given in the options is correct whose output is LOW, if and only if all the inputs are HIGH?
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Answer: C. NAND
A NAND gate outputs LOW only when all inputs are HIGH; in all other cases it outputs HIGH. This is the inverse of an AND gate. The AND gate outputs HIGH when all inputs are HIGH (opposite of what we need). OR and XNOR do not satisfy this condition.
Step-by-step Derivation:
Truth table analysis for a 2-input gate:
AND gate:
- Input (0,0) → Output 0
- Input (0,1) → Output 0
- Input (1,0) → Output 0
- Input (1,1) → Output 1 (HIGH when all HIGH)
NAND gate (NOT AND):
- Input (0,0) → Output 1
- Input (0,1) → Output 1
- Input (1,0) → Output 1
- Input (1,1) → Output 0 (LOW when all HIGH) ✓
OR gate:
- Input (1,1) → Output 1 (HIGH, not LOW)
XNOR gate:
- Input (1,1) → Output 1 (HIGH, not LOW)
Only NAND produces LOW output when all inputs are HIGH.