Answer:
![\huge\boxed{Radiation}](https://img.qammunity.org/2021/formulas/physics/high-school/qzjtgkj4r95xocc9og4gpv7tv9rq7jb05h.png)
Step-by-step explanation:
In microwave, there are waves called "microwaves" as per the name. So, The heating of food is done with the help of waves. Radiation is "the transfer of heat through waves". That is why the process of heating food in a microwave is "Radiation".