The working of a microwave oven involves

The working of a microwave oven is primarily based on the absorption of microwave radiation by matter, specifically water molecules within food [3]. Microwaves are non-ionizing electromagnetic waves that interact with matter on a macro scale. When food is placed in the oven, the microwave frequency is selected to be strongly absorbed by water molecules, causing them to rotate and vibrate rapidly [1]. This molecular movement generates thermal energy through friction, leading to the heating of the food [3]. While body tissues and food behave as lossy dielectrics, the dielectric properties are largely determined by water content, which facilitates this strong coupling and energy transfer [2]. Other options like MASER (microwave amplification by stimulated emission of radiation) or transmission through metal do not describe the heating mechanism; in fact, metals typically reflect microwaves rather than absorbing them for heating.

Sources

1. [1] https://oms.bdu.ac.in/ec-colleges/admin/contents/175_16SNMEEL2_2020052005400715.pdf
2. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 6: Environmental Issues > Horr{ the cell phone tower's radiation affects human? > p. 122
3. [2] https://www.sciencedirect.com/topics/physics-and-astronomy/microwave-amplifier