The condition under which a microwave oven heats up a food item containing water molecules most efficiently isa. The frequency of the microwave must match the resonant frequency of the water molecule.b. The frequency of the microwave has no relation with the natural frequency of the water.c. Microwaves are heat waves so they always provide heating.d. Infra-red waves produce heating in the microwave oven.

The condition under which a microwave oven heats up a food item containing water molecules most efficiently is:

a. The frequency of the microwave must match the resonant frequency of the water molecule.

Microwave ovens operate at a frequency of around 2.45 gigahertz (GHz), which happens to be very close to the resonant frequency of water molecules. When microwaves with this frequency are used, water molecules in the food absorb the microwave energy, causing them to vibrate and generate heat through friction. This is why microwaves are effective at heating food items that contain water molecules.