According to Graham's law at a given temp, the ratio of diffusion ${\mathrm{r}}_{\mathrm{A}}/{\mathrm{r}}_{\mathrm{B}}$ of gases $\mathrm{A}$ and $\mathrm{B}$ given by

As per the Graham's law for a given temperature $\mathrm{r}\propto \frac{\mathrm{P}}{\sqrt{\mathrm{M}}}$

It is provided in question that, $\mathrm{P}$ is the pressure of gas and $\mathrm{M}$ is its molar mass.

So, the ratios of the rates of diffusion $\frac{{\mathrm{\gamma }}_{\mathrm{A}}}{{\mathrm{\gamma }}_{\mathrm{B}}}$ of gases $\mathrm{A}$ and $\mathrm{B}$ can be represented by the expression:

$\frac{{\mathrm{\gamma }}_{\mathrm{A}}}{{\mathrm{\gamma }}_{\mathrm{B}}}=\frac{{\mathrm{P}}_{\mathrm{A}}}{{\mathrm{P}}_{\mathrm{B}}}·{\left(\frac{{\mathrm{M}}_{\mathrm{B}}}{{\mathrm{M}}_{\mathrm{A}}}\right)}^{1/2}$