A vessel contains mono atomic 'He' at 1 bar and 300 K, determine its number density -

$2.4\times {10}^{25 }{\mathrm{m}}^{-3}$

 $$\begin{gathered} \mathrm{Number} \mathrm{density}=\frac{\mathrm{P}}{\mathrm{kT}} \\ =\frac{1\times {10}^5\mathrm{pascals}}{1.38\times {10}^{-23}\mathrm{J}\times 300} \end{gathered}$$

 (where, k = Boltzmann constant)