Chemistry - Real Gas Question with Solution | TestHub

$He$ (top curve) shows no dip. $C{H}_4$ (lowest curve) dips deeply because its attractions are strong.

The '?' curve dips slightly, so it has moderate attractions: $N_2(a=1.39)$ fits.

$H_2$ would lie close to $He$ with no dip, while $N{H}_3$ and $C{O}_2(a=4.2$ and 3.6) would dip more than $C{H}_4(a=2.3)$.

Answer: (B).