Answer to Question #46441 in Inorganic Chemistry for pallavi

Microwaves with long wavelengths cause molecules to rotate faster when they are absorbed. Polar bonds in molecules like water and sugar act as handles for the microwave radiation to grab on to, and the rotational energy can be greatly increased by short exposures to microwaves. This fact explains why polar molecules heat up quickly in microwave ovens. By measuring the wavelength of absorption through microwave spectroscopy, the size of the molecule could be determined.

i) microwave inactive. CO2 molecule is linear and non-polar, so it doesn't absorb microwaves.
ii) microwave active. SnCl2 has angular structure and is polar, thus it is microwave active.
iii) microwave inactive. CBr4 is tetrahedral and non-polar, it doesn't absorb microwaves.