Answer: (D) no magnetic core loss.
Explanation:
Magnetic core losses consist of hysteresis loss and eddy current loss. Hysteresis loss is associated with ferromagnetic property of iron and eddy current loss is associated with conducting property of iron. As the air is not a ferromagnetic substance as well as it is not a conductor so there will not be any core loss in the air core transformer.
Air-core transformers are designed to transfer radio-frequency currents—i.e., the currents used for radio transmission; they consist of two or more coils wound around a solid insulating substance or on an insulating coil form. Iron-core transformers serve analogous functions in the audio-frequency range.