Which of the following is an inverter gate?

The correct output for the given logic circuit and inputs is:

The symbolic representations of four logic gates are given below. The logic symbols for $OR$,$NOT$,and $NAND$ gates are respectively:

Six logic gates are connected as shown in the figure. The values of $y_1, y_2$ and $y_3$ respectively are

The following figure shows a logic gate circuit with two inputs $A$ and $B$ and the output $Y.$ The voltage waveforms of $A, B$ and the output $Y$ are as given in the diagram. The logic gate is $:-$

In the following circuit, what are the values of $P$ and $Q$?