All gases except __________ shows a cooling effect during throttling process at atmospheric temperature and pressure.

Answer: Option D

Since all the gases except $$H_2$$ $$He$$ etc, have maximum inversion point greater than atmospheric (room) temperature cooling can take place by throttling if the initial conditions lie in a region where joule thomson coefficient is positive. But for $$H_2$$ the maximum inversion point is very low so usually heating takes place by throttling. But if we do the decrease the temperature of $$H_2$$ from room temperature to below the maximum inversion point temperature by some primary cooling techniques than there are chances where cooling of $$H_{2gas}$$ can be done by throttling.