Question

A digital circuit which compares two numbers $A_3{A}_2{A}_1{A}_0,B_3{B}_2{B}_1{B}_0$ is shown in figure. To get output $Y=0$, choose one pair of correct input numbers.

Answer 1

For a $4-$input $X-NOR$ gate, output will be zero if number of $1$'s will be odd.
We also know that output of $XOR$ gate will be ${}^{\prime }{1}^{\prime }$ if number of $1$'s will be odd. If the inputs will be same then output of $XOR$ gate will be $0$ so all inputs to $XNOR$ will be zero so output $Y$ will be ${}^{\prime }{1}^{\prime }$. So only in option (d) the inputs are different so $Y$ will be zero.