An atom or molecule of a gas has a size of the range 50 to 200 nm(Nanometer). If you consider the volume of gas molecule, it will be of the range 10 to the power -21 litre. So volume of gas molecule is almost negligible when compared with 22.4 liters of volume at 273.15 K and 1 atm pressure of the system. In addition to that , gas molecules are considered as point masses as per kinetic theory of gases.
So 22.4 litres of volume is the volume of system rather than gas molecules at 273.15 K temperature and 1 atm pressure.
So volume of all gases is same at 273.15 K and 1 atmospheric pressure.
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