Mechanical Engineering - Thermodynamics - Discussion

Internal energy is a function of temperature only for the Ideal gas.

Option B is correct.

The average velocity and molecular activities are directly proportional to the temperature of the gas of the system and as a result of the system leads to higher internal energy. So there are no changes in internal energy in an isothermal process, what internal energy referred here in thermodynamics is (microscopic forms of energy example; electron spin, nuclear spin, molecular vibrations), so microscopic interactions of molecular activities occur only if there is a change in temperatures.