A gaseous mixture contains ${\mathrm{CO}}_2\left(\mathrm{g}\right)$ and${\mathrm{N}}_2\mathrm{O}\left(\mathrm{g}\right)$in 2 : 5 ratio by mass. The ratio of the number of molecules of ${\mathrm{CO}}_2\left(\mathrm{g}\right)$ and${\mathrm{N}}_2\mathrm{O}\left(\mathrm{g}\right)$ is