Which overlap results in the formation of the strongest bond?

Which among the following represents zero overlap?

Calculate the ratio of $\sigma$ and $\pi$ bonds for the following compounds and determine the correct order:
$A$: Tetracyanomethane $(C(CN)_4)$
$B$: Carbon dioxide $(CO_2)$
$C$: Benzene $(C_6H_6)$
$D$: $1, 3$-Butadiene $(CH_2=CH-CH=CH_2)$

Which of the following orbital combinations form a sigma $(\sigma)$ bond? $1s-1s, 2s-2s, 1s-2s, 2p_x-2p_x, 2p_y-2p_y, 2p_z-2p_z$.

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

Considering the $x$-axis as the internuclear axis,which of the following will not form a sigma $(\sigma)$ bond and why?
$(a)$ $1s$ and $1s$
$(b)$ $1s$ and $2p_{x}$
$(c)$ $2p_{y}$ and $2p_{y}$
$(d)$ $1s$ and $2s$