Explanation

(c) In a transformer
Iron losses In actual iron cores, inspite of lamination, eddy current are produced. The magnitude of eddy current may however be small and a part of energy is lost as the heat produced in the iron core.
Copper losses In practice, the coils of the transformer possess resistance. So, a part of the energy is lost the due to the heat produced in the resistance of the coil.
Flux leakage The coupling between the coils is seldom perfect. So whole of the magnetic flux produced by the primary coil is not linked up with the secondary coil.
And hysteresis loss, humming losses also occur in the transformer.