The gas that would diffuse the fastese is HYDROGEN, H2.
Factors that affect the rate of diffusion of a gas include: the density of the gas, temperature, concentration difference and diffusion distance. The density of the diffusing gas depends on how light or how heavy the gas is. Looking at all the options given above, it will be observed that it is hydrogen that has the lightest weight, as indicated by its atomic mass and thus it will diffuse faster than any of the remaining compounds.