Consider hydrogen molecules as spheres of radius $1 Å$. So, $r=1 Å=$ radius $=10^{-10} \mathrm{~m}$ Volume of hydrogen molecules $=\frac{4}{3} \pi r^3$ $\begin{aligned} \text { Volume of } 1 \text { molecule } &=\frac{4}{3}(3.14)\left(10^{-10}\right)^3 \\ &=4 \times 10^{-30} \mathrm{~m}^3 \end{aligned}$
Number of moles is $0.5 \mathrm{~g}$ of $\mathrm{H}_2$ gas
$$
\begin{aligned}
&=\frac{\text { Mass }}{\text { Molecular mass }} \\
&=\frac{0.5}{2}=0.25 \text { mole }\left(\mathrm{H}_2 \text { has } 2 \text { mole }\right)
\end{aligned}
$$
Molecules of $\mathrm{H}_2$ present
$=$ Number of moles of $\mathrm{H}_2$ present $\times 6.023 \times 10^{23}$
$=0.25 \times 6.023 \times 10^{23}$
$\therefore$ Volume of $\mathrm{H}_2$ molecules
$=$ number of molecules $\times$ volume of each molecule
$=0.25 \times 6.023 \times 10^{23} \times 4 \times 10^{-30} \mathrm{~m}^3$
$=6.023 \times 10^{23} \times 10^{-30} \approx 6 \times 10^{-7} \mathrm{~m}^3$
Now for ideal gas at constant temperature is considered to be constant
$$
p_i V_i=p_f V_f
$$
$\begin{aligned} V_f &=\left(\frac{p_i}{p_f}\right) V_i=\left(\frac{1}{100}\right)\left(3 \times 10^{-2}\right)^3 \\ &=\frac{27 \times 10^{-6}}{10^2}=2.7 \times 10^{-7} \mathrm{~m}^3 \end{aligned}$
$\left(\therefore\right.$ Volume of cube $V_i=(\text { Side })^3$ and $p_i=1$ atm at NTP. $)$ Hence on compression the volume of the gas is of the order of the molecular volume [from Eq. (i) and Eq. (ii)]. If the intermolecular forces will play the role as in kinetic theory of gas, molecules do not interact each other so gas will deviate from ideal gas behaviour.