How many $\sigma$ and $\pi$ bonds are there in the molecule of tetracyanoethylene $(CN)_2C=C(CN)_2$?

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

Draw diagrams showing the formation of a double bond and a triple bond between carbon atoms in $C_2H_4$ and $C_2H_2$ molecules.

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Zero orbital overlap is an out-of-phase overlap.
Reason $R$: It results due to different orientation/direction of approach of orbitals.
In the light of the above statements,choose the correct answer from the options given below.

Among the following ions,the $p\pi - d\pi$ overlap could be present in:

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 $2s$