$(A)$ The average energy per mole of the gas mixture is $2RT$.
$(B)$ The ratio of speed of sound in the gas mixture to that in helium gas is $\sqrt{6 / 5}$.
$(C)$ The ratio of the rms speed of helium atoms to that of hydrogen molecules is $1 / 2$.
$(D)$ The ratio of the rms speed of helium atoms to that of hydrogen molecules is $1 / \sqrt{2}$.

$(I)$ Energy of one molecule at absolute temperature is zero
$(II)$ $r .m.s.$ speeds of different gases are same at same temperature
$(III)$ For one gram of all ideal gas kinetic energy is same at same temperature
$(IV)$ For one mole of all ideal gases mean kinetic energy is same at same temperature