The term that accounts for intermolecular force in Van der Waals equation for non-ideal gas is

Why do real gases deviate from ideal behavior in the $pV$ vs $p$ and $p$ vs $V$ graphs at specific temperatures?

$A$ gas is said to behave like an ideal gas when the relation $PV/T = \text{constant}$. When do you expect a real gas to behave like an ideal gas?

Assertion : Greater the value of van der Waal's constant $a$,greater is the liquefaction of gas.
Reason : $a$ indirectly measures the magnitude of attractive forces between the molecules.

Real gases deviate from ideal behaviour because the molecules

For which of the following gases is the value of the van der Waals constant $'a'$ expected to be the highest?