What is XNOR logic gate?

Boolean relation at the output stage- $Y$ for the following circuit is:

In the following digital circuit, what will be the output at $\mathrm{Z}$, when the input $\left(\mathrm{A},\mathrm{B}\right)$ are  $\left(1,0\right), \left(0,0\right), \left(1,1\right), \left(0,1\right)$

Given, $A$ and $B$ are input terminals

Logic $1$ is$>5 \mathrm{V}$

Logic $0$ is$<1 \mathrm{V}$

Which logic gate operation, the following circuit does?

Note: This question was awarded a bonus. $C$ option changed. 

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

The logic gate equivalent to the given logic circuit is:

Which of the following gates will have an output of $1$?

Identify the operation performed by the circuit given below :

Identify the correct output signal $Y$ in the given combination of gates (as shown $n$) for the given inputs $A and B$

In the following circuit what are $P$ and $Q$ :