Graham’s Law of Diffusion states that provided the temperature and pressure are constant, that the rate of diffusion of gas is inversely proportional to the square root of its density.
R ∝ 1/√e
R1R2 = √(e2/e1)
Since relative molecular mass = 2 x density
i.e M = 2e
R1R2 = √(M2/M1)