Correct option is D
The maximum efficiency of a transformer occurs when the core losses (also known as iron losses) are equal to the copper losses. Core losses are constant and do not vary with load, while copper losses vary with the square of the load current.
The condition for maximum efficiency is derived from the fact that efficiency is maximized when the total losses are minimized. This happens when:
Thus, the correct answer is (d) Core loss = Copper loss.
