Assuming that $O_2$ molecule is spherical in shape with radius $2\text{Å}$ the percentage of the volume of $O_2$ molecules to the total volume of gas at S.T.P. is

Let 1 mole of $O_2$ is taken 1 mole of an ideal gas occupies 22. 7 L at STP.

Volume of 1 mole molecules $=\frac{4}{3}\pi r^3\times N_A$

$\begin{array}{l}=\frac{4}{3}\times \pi \times 2^3\times {10}^{-24}\times 6.02\times {10}^{23}\times {10}^{-3}\mathrm{L}\\ \simeq 2\times {10}^{-2}\mathrm{L}\\ \mathrm{\%}=\frac{2\times {10}^{-2}}{22.7}\times 100=0.09\mathrm{\%}\end{array}$