In which of the following ions is $p\pi - d\pi$ overlap present?

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 represents the nodal plane in the $\pi$-bond of ethene $(C_2H_4)$?

State the number of $\sigma$ and $\pi$ bonds in the following molecules:
$(a)$ $C_2H_2$
$(b)$ $C_2H_4$

The fluorine molecule is formed by

Which among the following represents zero overlap?