Here, the diameter of an oxygen molecule, d=3Å=3×10–10m
The radius of an oxygen molecule
r=

d

2

=

3×10−10

2

m
Molecular volume of one mole of oxygen, V′
= Volume of one molecule of oxygen × Avogadro number(N)
=

4

3

πr3×N
=8.52×10−6m3
Actual volume occupied by one mole of oxygen gas at S.T.P.V=22,400cm3
=22,400×10–6m3
∴ Fraction of molecular volume of the actual volume occupied by
O2=

V′

V

=

8.52×10−6

22,400×10−6

=3.8×10−4≃4×10−4