The $NOR$ gate is a combination of which two gates?

The output $Y$ for the inputs $A$ and $B$ of the circuit is given by the truth table of the shown circuit:

How many $NAND$ gates are used to form an $AND$ gate?

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 $Z$?

Which one of the following logic gates is called a Universal gate?

In the following logic circuit,the sequence of the inputs $A, B$ are $(0,0), (0,1), (1,0)$ and $(1,1)$. The output $Y$ for this sequence will be: