An ideal gas is pressed at constant temperature. Its internal energy:

Explanation

The correct answer is D: Remains the same. For an ideal gas, internal energy is a function of temperature only (U ∝ T). Since the temperature is constant, the internal energy does not change. Option A is incorrect because a decrease in internal energy would require a decrease in temperature, which is not happening. Option B is incorrect because there is no fluctuation in temperature, hence no fluctuation in internal energy. Option C is incorrect because an increase in internal energy would require an increase in temperature, which is also not happening.In summary, for an ideal gas undergoing a process at constant temperature, the internal energy remains constant because it is directly proportional to temperature, and no temperature change occurs.