Four one liter flasks are separately filled with the gases $O_2,f_2,CH_4$ and $CO_2$ under the same conditions. The ratio of number of molecules in these gases.

Question

$\begin{array}{1 1} 2:2:4:3 \\ 1:1:1:1 \\ 1:2:3:4 \\ 2:2:3:5 \end{array} $