Which of the following symbols represent the NOR gate?

Concept: A logic gate's identity is fixed by its truth table — the output it produces for every input combination — not by the base shape used to draw it. The standard NOR symbol is an OR-body gate (curved input side, pointed output side) with an inversion bubble at its output. Separately, De Morgan's theorem states NOT(A) AND NOT(B) = NOT(A OR B), so an AND-body gate with an inversion bubble on every input realizes the same output function as a NOR gate, even though it is drawn from a different base shape.

Application:

1. Symbol I is an OR-body gate (curved input side, pointed output side) with one inversion bubble at the output — by definition, this is the standard NOR gate symbol.

2. Symbol II is an AND-body gate (flat input side, rounded output side) with an inversion bubble on each of its two inputs — it represents NOT(A) AND NOT(B).

3. Applying De Morgan's theorem to symbol II: NOT(A) AND NOT(B) equals NOT(A OR B), which is exactly the NOR function — so symbol II also realizes NOR, built from an AND-based shape instead of an OR-based one.

Cross-check: Building the truth table for both expressions across all four input combinations confirms the equivalence:

The NOR column and the NOT(A) AND NOT(B) column match on every row, confirming symbol II produces the identical output to symbol I for every input combination — both symbols represent the NOR gate.