Power loss in a transformer is known as the _______.

Correct option is D

The power loss in a transformer is known as the difference of power between the primary and the secondary coils. 
Transformers have some energy loss, so the output power is always less than the input power. This is because of the following types of losses: 
· Resistive loss: Also known as copper loss or ohmic loss, this is caused by the resistance of the copper wire used to make the windings. The power is dissipated as heat. 
· Load losses: These losses are associated with the coils. 
· No-load losses: These losses are produced in the core.