Gases deviate from the ideal gas behaviour because their molecules:
Possess negligible volume
Have forces of attraction between them
Are polyatomic
Are not attracted to one another
As we learnt in Behaviour of real gas - attraction forces exist between molecules at low temperature.
Because molecules of real gases have intermolecular forces of attraction so the effective impact on the wall of the container is diminished. Pressure of real gas is reduced by factor hence behaviour of real gas deviate from ideal behaviour.
Option (b) is correct