Answer:
D. The process in which a substance gains energy
Explanation:
An endothermic reaction is a reaction in which heat energy is absorbed from the surroundings therefore we can imply that in such reaction, the substances gains energy. In endothermic reactions, the surrounding becomes colder at the end of the changes.
Here, the heat energy level of the final state is higher than that of the initial state. Most dissolution reactions are endothermic in nature. Examples are dissolution of Sodium chloride in water.
Note: it is in exothermic reaction that heat energy is liberated to the surrounding
