What defines a precipitation reaction?

A precipitation reaction is characterized by the formation of an insoluble solid, known as a precipitate, when two aqueous solutions are combined. In this type of reaction, the reactants, usually soluble salts in solution, react together, leading to the formation of a product that cannot remain dissolved in the solution. This solid precipitate will settle out from the solution over time.

This defining feature is central to recognizing precipitation reactions in chemistry. For example, when mixing solutions of silver nitrate and sodium chloride, a white precipitate of silver chloride forms, showcasing the key characteristic of this reaction type. The process often involves ionic compounds where the ions interact to create a new compound that has low solubility in water.

The other options describe different types of reactions or processes that do not meet the specific criteria of a precipitation reaction. A gas formation, high temperatures, or energy release in the form of light pertain to other chemical reaction classifications and do not specifically indicate that a solid precipitate is formed. Thus, option B correctly captures the essence of what defines a precipitation reaction.