When a completely compensated inverting amplifier is nulled at room temperature 25°C, the total output offset voltage becomes zero again at a different temperature due to thermal drift. The correct answer is (a) 50°C. The amplifier's compensation is designed for the nulling temperature, but due to thermal drift effects on the op-amp characteristics, the offset voltage changes with temperature. At approximately 50°C, the compensated drift equals the original offset in opposite direction, making the total output offset voltage zero again.