Reacts

Reacts is the third-person singular present tense of the verb to react. It denotes responding to a stimulus, to a situation, or to the actions of others. The form is used with he, she, or it, as in "the substance reacts when heated" or "she reacts quickly to feedback." The word derives from Latin reagere, re- "again" and agere "to act," via Old French.

In chemistry, a reaction occurs when substances undergo chemical change as a result of interaction. A substance A reacts with a substance B to form products C and D. Reactions can be classified by mechanisms, energy changes, and whether they release heat (exothermic) or absorb heat (endothermic), and whether catalysts are involved.

In biology and physiology, reactions describe how organisms respond to stimuli: a reflex, hormonal release, or metabolic adjustment. In psychology and everyday language, a person's reaction is an emotional or cognitive response to an event.

In economics and social sciences, market or public reactions describe how groups respond to news, policy, or social change. The term emphasizes the act of responding rather than the initial cause, and it is widely used across scientific and everyday discourse.