\( = \frac{5}{2}\,\,\frac{M}{{{M_0}}}RT\left( {\because \mu = \frac{M}{{{M_0}}}} \right) = \frac{5}{2} \times M \times \frac{P}{\rho }\left( {\because \frac{{RT}}{{{M_0}}} = \frac{1}{\rho }} \right) = \frac{5}{2} \times 1 \times \frac{{8 \times {{10}^4}}}{4} = 5 \times {10^4}\,J\)