Final answer:
Molecular rotation occurs in the microwave region of the electromagnetic spectrum.
Step-by-step explanation:
The answer to the question 'Molecular rotation occurs in what region of the electromagnetic spectrum?' is d) Microwave.
Molecular rotation refers to the rotation of molecules around their center of mass. It can be induced by the absorption of microwave photons, which have wavelengths in the range of 1 millimeter to 1 meter. These photons provide the necessary energy to promote molecular rotation. In contrast, other regions of the electromagnetic spectrum, such as infrared, ultraviolet, and X-ray, are known for their effects on other molecular processes like vibration and electronic transitions.