Diffusion in the ability of a gas to spread and occupy the whole available volume irrespective of other gases present in the container.Thomas Graham in 1831 proposed the law of gaseous diffusion.The law states that under similar conditions of temperature and pressure, the rates of diffusion of gases are inversely proportional to the square roots of their densities.Mathematically Graham’s Law of Diffusion / Effusionr ∝ 1 / √dwhere r is the rate of diffusion and d is the density of the gas.