What term is defined as the amount of heat required to convert a unit mass of a substance from a liquid to a vapor at constant temperature and pressure?

Correct Answer: Option D — Latent heat of vaporization

Latent heat of vaporization is the energy required to change a substance from liquid to vapor at a constant temperature and pressure. This phase change occurs without a temperature increase, a critical concept in boiler operation, condenser performance, and refrigeration cycle thermodynamics.