Which of the following defines an endothermic reaction?

An endothermic reaction is defined by its ability to absorb heat from the surroundings. When an endothermic reaction occurs, the system takes in energy, typically in the form of thermal energy. This absorption leads to a decrease in the temperature of the surroundings if not compensated by another source of heat. A common example of an endothermic process is the dissolution of certain salts in water or photosynthesis in plants, where energy from sunlight is absorbed.

In contrast, the other choices describe different types of energy dynamics. Reactions that release heat to the surroundings are classified as exothermic, while spontaneous reactions may or may not involve heat exchange and often depend on changes in entropy, temperature, and the Gibbs free energy. Reactions with no energy change are generally static and not representative of typical chemical reactions involving energy transfer. Thus, the correct understanding of endothermic reactions focuses on their nature of heat absorption from the surroundings.