Toasting bread involves the transformation of

1. electrical energy into mechanical energy

2. electrical energy into thermal energy

3. thermal energy into electrical energy

Option (b) is correct.

The toaster uses the electrical energy and converts that into thermal (heat) energy. the total energy remains constant, we can just transform it from one form to another. the toaster has resistance coils in which the electrical energy gets dissipated in the form of heat. That heat energy then roasts the bread.

Thus in toaster, electrical energy is converted into thermal energy.

the second option, Electric into Thermal