a mixture of h2 and he at 300 k effuses from a tiny hole in the vessel that contains it. what is the mole fraction of h2 in the original gas mixture if 3.00 times as many he atoms as h2 molecules escape from the orifice in unit time? if the same mixture is to be separated by a barrier- diffusion process, how many stages are necessary to achieve h2 of 99.9% purity?