Four one litre flasks are separately filled with gasses ${\mathrm{O}}_2$, ${\mathrm{F}}_2$, ${\mathrm{CH}}_4$ and ${\mathrm{CO}}_2$ under same conditions. The ratio of number of molecules in these gases

According to Avogadro's law, the samples of an inert gas, of the same volume and temperature and at same pressure, have equal number of molecules.

Therefore, all the flasks would have the same no. of molecules.

∴ Ratio of no. of molecules of ${\mathrm{O}}_2$,${\mathrm{F}}_2$,  ${\mathrm{CH}}_4$ and ${\mathrm{CO}}_2$ is 1:1:1:1.

Hence, the required option is B.