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## QuestionPhysicsClass 11

A gas mixture consists of $$2\:mol$$ of oxygen and $$4\:mol$$ of argon at temperature $$T$$. Neglecting all vibrational modes, the total internal energy of the system is
(A) $$4RT$$
(B) $$15RT$$
(C) $$9RT$$
(D) $$11RT$$

$$O_2$$ molecule has 3 translational and 2 rotational degrees i.e total of 5 degrees of freedom.
Since Argon is a noble gas, it consists only of atoms and the energy is purely translational kinetic energy.
Total internal energy: $$U = 2 \times \dfrac{5}{2}RT + 4 \times \dfrac{3}{2}RT = 11RT$$