A mixture of oxygen with hydrogen has a volume of 45 liters and contains 0.9 mol

A mixture of oxygen with hydrogen has a volume of 45 liters and contains 0.9 mol of oxygen. The volume fraction of oxygen in the mixture is?

Regardless of the nature of gases, under normal conditions they all occupy the same volume, depending only on the amount of substance, such a volume is called molar – Vm = 22.4 l / mol.
The volume fraction of gas in the mixture ϕ = Vg / Vcm, where Vg is the gas volume, and Vcm is the volume of the gas mixture. In turn, Vg = Vm * n (g), where n (g) is the amount of substance of this gas.
Substitute this expression into the first formula ϕ = Vm * n (g) / Vcm and calculate the volume fraction of oxygen in the mixture ϕ (О2) = 22.4 * 0.9 / 45 = 0.448 or 44.8%