In the given circuit,$A$ and $B$ are two inputs and $C$ is the output. Which logic gate does this circuit represent?

The figure below shows a combination of $NOT$ gates and a $NOR$ gate. The combination is equivalent to:

If $X$ and $Y$ are the inputs, the given circuit works as . . . . . . .

In the given circuit,the output $Y$ becomes zero for the inputs

In the circuit shown in the following figure,the value of $y$ is:

The circuit diagram shows a logic combination. Initially, for inputs $P, Q, R$ and $S$ all at state $1$, the outputs are $X=1, Y=1$ and $Z=0$. When inputs $P$ and $R$ change to state $0$ while inputs $Q$ and $S$ remain at state $1$, what are the new states of outputs $X, Y$ and $Z$?