To find total energy for a given molecule of a gas, we must find the number of degree of freedom.
The molecule of oxygen has 2 atom.
So it has $(3 T+2 R)=5$ degree of freedom.
So $\mathrm{O}_2$ is a diatomic gas having 5 degrees of freedom. Energy (total internal) per mole of the gas $=\frac{5}{2} R T \quad[R=$ Universal gas constant, $T=$ temperature $]$ For 2 moles of the gas total internal energy $=2 \times \frac{5}{2} R T=5 R T$
Neon (Ne) gas is a monoatomic so its degrees of freedom is only 3 . Hence total internal energy per mole $=\frac{3}{2} R T$ so total internal energy of 4 moles of $\mathrm{Ne}$.
Energy $=4 \times \frac{3}{2} R T=6 R T$
[Using Eqs. (i) and (ii)] Hence total internal energy of 2 mole oxygen and 4 mole Ne.
$$
\therefore \text { Total energy }=5 R T+6 R T=11 R T \text {. }
$$