From a certain apparatus, the diffusion rate of hydrogen has an average value of 28.7 `cm^3` `s^(–1)`. The diffusion of another gas under the same conditions is measured to have an average rate of 7.2 `cm^3` `s^(–1)`. Identify the gas. [Hint : Use Graham’s law of diffusion: R1/R2 = ( M2 /M1 )1/2, where R1, R2 are diffusion rates of gases 1 and 2, and M1 and M2 their respective molecular masses. The law is a simple consequence of kinetic theory.]