A gas mixture consists of 2 moles of O₂ and 4 moles of Ar at temperature T. Neglecting all vibrational modes, the total internal energy of the system is :

11 RT

Total internal energy of the system is given by

U = n₁ \(\frac{f_1}{2}\) RT + n₂ \(\frac{f_2}{2}\) RT

As oxygen is diatomic therefore its degree of freedom would be 5
whereas for monoatomic argon degree of freedom is 3

   = 2 x \(\frac{5}{2}\) RT + 4 x \(\frac{3}{2}\) RT

   = 11 RT