Answer: Radiation
Explanation: There are three modes of heat transfer:
1. Conduction: This type of heat transfer happens when there is direct contact between the two object.
2. Convection: This type of heat transfer happens when there is a movement of fluid (liquid or gas).
3. Radiation: This type of heat transfer happens when there is direct transfer of energy through electromagnetic waves through space.
In Microwave, the electromagnetic waves are produced in microwave frequency range which are used to heat the water molecules which further heat the food.