Final answer:
The correct answer is option A. When molecules move less rapidly, the heat energy of a body is reduced due to the decrease in molecular kinetic energy which is associated with the temperature of the substance.
Step-by-step explanation:
When the molecules of a body move less rapidly, heat energy in the body is reduced.
The kinetic theory of matter states that as the temperature of a substance increases, the molecular movement or kinetic energy also increases. Conversely, when the temperature decreases, the molecules move more slowly and the substance loses heat energy. Therefore, the process of molecules moving less rapidly leads to a reduction of heat energy in the body.
Heat transfer and the relationship it has with molecular movement is essential to understanding how thermal energy is changed within a substance. When a body cools down, the average kinetic energy of the molecules decreases, leading to a reduction in the heat energy of the body.