Which of the following bonds is formed by the lateral overlap of $p-p$ orbitals?

What is the total number of sigma $(\sigma)$ and pi $(\pi)$ bonds in the following molecules?
$(a)$ $C_{2}H_{2}$
$(b)$ $C_{2}H_{4}$

In an acetylene molecule,the bond between the carbon atoms consists of:

Assuming the bond direction is along the $z$-axis,which of the following overlaps of atomic orbitals of two atoms $(A)$ and $(B)$ will result in bonding?
$I$. $s$-orbital of $A$ and $p_x$-orbital of $B$
$II$. $s$-orbital of $A$ and $p_z$-orbital of $B$
$III$. $p_y$-orbital of $A$ and $p_z$-orbital of $B$
$IV$. $s$-orbital of both $(A)$ and $(B)$

Which of the following statements is not correct?

Which type of overlapping results in the formation of a $\pi$ bond?