Physics · Heat and Thermodynamics

The internal energy of an ideal gas is determined by its temperature because it is directly related to the kinetic energy of its molecules. According to the kinetic theory of gases, the average kinetic energy of gas molecules is proportional to the absolute temperature of the gas. Pressure and volume do not directly affect the internal energy in an ideal gas scenario. Therefore, the correct answer is temperature, as the internal energy is a function of temperature alone in ideal gases. 

The internal energy of an ideal gas is independent of its pressure. It primarily depends on the kinetic energy of the gas molecules, which is a function of temperature, not pressure. Therefore, this option is incorrect. 

While volume affects the overall space the gas occupies, the internal energy of an ideal gas is not directly dependent on volume. It is mainly influenced by temperature. Thus, this option is incorrect. 

The internal energy of an ideal gas is directly proportional to its temperature. This is because the kinetic energy of gas molecules, which constitutes internal energy, increases with temperature. Hence, this option is correct. 

Since the internal energy of an ideal gas is independent of both pressure and volume, this option is incorrect. Internal energy depends solely on temperature.