The output of the given combination gates represents :

Solution

Physics sir · 3 steps

A NOR with its two inputs tied together is only a NOT gate. Spot that first and the circuit becomes easy.

1. Tied inputs. When both inputs of a NOR gate carry the same signal X, the output is X + X̅ = X̄. So the two input gates and the last gate each act as a NOT gate.
2. Middle gate. The middle NOR receives Ā and B̄. By De Morgan's theorem its output is Ā + B̄̅ = A · B, which is an AND.

   Y = Ā + B̄̅̅ = A · B̅

   A, B	Ā, B̄	Middle NOR = AB	Y
   0, 0	1, 1	0	1
   0, 1	1, 0	0	1
   1, 0	0, 1	0	1
   1, 1	0, 0	1	0

3. So. The output is 0 only when both inputs are 1, so Y = A · B̅. The circuit is a NAND gate, option (c).

The idea to keep. A NOR or NAND gate with its inputs shorted together is a NOT gate. Replace those gates with NOT first, then use De Morgan's theorem on what remains.

Answer from the NTA final answer key. Solution by PrepWiser.