A vessel contains a mixture of one mole of oxygen and two moles of nitrogen at 300 K. The ratio of the average rotational kinetic energy per O2 molecule to that per N2 molecule is

Kinetic energy per degree of freedom = 12kT. As diatomic gas possess two degree of freedom for rotational motion therefore rotational K.E.= 2(12kT) = kT . ln the problem both gases (oxygen and nitrogen) are diatomic and have same temperature (300 K) therefore ratio of average rotational kinetic energy will be equal to one.