Molar volume means that 1 mol of any gas occupies a volume of 22.4 L at standard temperature and pressure conditions.
the molar mass of Ar is 40 g/mol
this means that a mass of 40 g occupies a volume of 22.4 L
therefore a mass of 120 g of Ar occupies a volume of - 22.4 L / 40 x 120
therefore volume occupied by Ar - 67.2 L
