According to Graham's law of diffusion, the rate of diffusion is given by

$r\propto 1/\sqrt{M}$   Also  $r\propto p_{\mathrm{A}}$

where $p_A$ is the partial pressure of the constituent A in the mixture. Larger the partial pressure, larger the number of molecules striking the orifice through which diffusion occurs.

Hence, $\frac{r_{\mathrm{A}}}{r_{\mathrm{B}}}=\frac{p_{\mathrm{A}}}{p_{\mathrm{B}}}{\left(\frac{m_{\mathrm{B}}}{M_{\mathrm{A}}}\right)}^{1/2}$