Kinetic energy=1/2* MV(rms)^2….....1
Vrms= (3RT/M)^0.5........2
where R is universal gas constant ;T is temperature in kelvin and M is mass of a mole of substance in grams.
while calculating root mean square velocity, we get that it is inversly proportional to mass of gas. while in calculation of kinetic energy when we take sqaure of Vrms (as per the formula 1) the mass term gets cancelled out . Hence KE energy does not have a mass term . This does not mean that it is independent of mass.