A cylinder of compressed gas contains nitrogen and oxygen in the ratio 3:1 by mole. If the cylinder is known to contain $2.5\times {10}^4$ g of oxygen, what is the total mass of the gas mixture?

Number of moles of oxygen in the cylinder = $=\frac{\text{ Mass (in gram) }}{\text{ Molecular mass (in gram }\left.{\mathrm{mol}}^{-1}\right)}$

$=\frac{2.5\times {10}^4}{32}=781.25$

$\therefore$$\text{ Number of moles of }{\mathrm{N}}_2=3\times 781.25=2343.75$

Mass of nitrogen in the cylinder = $2343.75\times 28$

                                              = 65625 g = 6.5625x ${10}^4$g

Total mass of the gas in the cylinder $=2.5\times {10}^4+6.5625\times {10}^4$

                    $=9.0625\times {10}^4 \mathrm{g}$