The correct options are
C a(NH3)>a(N2) but b(NH3) <b(N2)
D The intermolecular force of attraction between the NH3 molecules > the force between N2 molecules
The value of a is the measure of the ability of the gas to get liquified easily
So,
a for (NH3)>a for (N2)
and b for (NH3)<b for (N2)
Also, the intermolecular force of attraction between NH3 molecules > the force between N2 molecules