The given circuit works as:

Solution

Physics sir · 3 steps

A NOR gate with its inputs tied together is only a NOT gate, so follow the signal through each stage.

1. Tied inputs. When both inputs of a NOR gate carry the same signal X, the output is X + X̅ = X̅. So the first two gates turn A into A̅ and B into B̅, and the last gate inverts whatever reaches it.
2. Middle gate. The middle NOR receives A̅ and B̅. By De Morgan's theorem, A̅ + B̅̅ = A · B, so this stage gives AND. The final NOT then inverts it.

   Y = A̅ + B̅̅̅ = A · B̅

   A	B	A̅, B̅	Middle NOR	Output 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, and 1 otherwise. That is the truth table of a NAND gate, option (d).

The idea to keep. NOR with tied inputs is NOT. Inverting both inputs of a NOR gives AND, and inverting both inputs of a NAND gives OR. Track the circuit stage by stage, then check your result against the truth table.

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