During an isothermal expansion of an ideal gas at constant temperature, which thermodynamic quantity remains completely unchanged?

💡 Solution & Explanation

In an isothermal process, the temperature of the ideal gas remains constant. Since internal energy of an ideal gas depends solely on its absolute temperature, the internal energy does not change during this process. Although pressure and volume change inversely according to Boyle law, entropy increases because heat is absorbed from the surroundings to maintain thermal equilibrium.