The rates of diffusion of gases are inversely proportional to square root of their densities . This statement refers to:

Graham's law states that the rate of diffusion of a gas is inversely proportional to the square root of its molecular weight. n the same conditions of temperature and pressure, the molar mass is proportional to the mass density. Therefore the rate of diffusion of different gases is inversely proportional to the square root of their mass densities.

$$\begin{gathered} \mathrm{r} =\frac{1}{\sqrt{\mathrm{d}}} \\ \mathrm{r} =\frac{1}{\sqrt{\mathrm{M}}} \end{gathered}$$