Logic Gates question from JEE Main 2013 (23 Apr, Shift 1)

Answer: (a)

1. First NOR: $N = \overline{A + B}$. Then $\overline{A + N}$ and $\overline{B + N}$, then a final NOR.
2. $00$: $N = 1$, both middle outputs 0, $Y = 1$.
3. $01$: $N = 0$, middle outputs $\overline{0} = 1$ and $\overline{1} = 0$, $Y = 0$; similarly $10 \to 0$.
4. $11$: $N = 0$, both middle outputs 0, $Y = 1$. This is XNOR.
5. Output column $1, 0, 0, 1$. So the answer is (a).