During the process of generating electricity, what transfers energy from the fuel to the water in a kettle?

In the process of generating electricity, the correct response is heat, as it is the medium through which energy is transferred from the fuel to the water in a kettle. When fuel is burned, it generates thermal energy (heat), which warms up the water in the kettle to convert it into steam or to simply heat it for various uses. This transfer occurs as the thermal energy from the combustion of the fuel is conducted through the walls of the kettle into the water.

In this scenario, other options such as waves and smoke do not effectively describe the method of energy transfer relevant to heating water in a kettle. Electric current relates to the transfer of electrical energy and is applicable in electric kettles where electricity heats the water by passing through a resistive element. However, in the context of the question focusing on fuel as the source, heat is the main energy transfer mechanism.