In circuit in following fig. the value of $Y$ is

Question

Professor PC Thomas Classes · Answer

Lower NOT gate inverts input to zero. NOT gate from NAND gate inverts this output to 1 upper NAND gate converts this input 1 and input 0 to 1 .
Thus $A \doteq 1$ and $B=1$ become inputs of NAND gate giving final output as zero. Choice $A$ is correct.