The condition under which a microwave oven heats up a food item containing water molecules most efficiently in
(a) the frequency of the microwave must match the resonant frequency of the water molecules
(b) the frequency of the microwave has no relation with natural frequency of water molecules
(c) microwave are heat waves, so always produce heating
(d) infrared waves produce heating in a microwave oven
(a) It is electromagnetive wave,therefore the correct choice is (a).