Which statement accurately describes a reactant in a chemical reaction?

A reactant in a chemical reaction is a substance that undergoes a transformation during the process, leading to the formation of products. This transformation typically involves breaking and forming chemical bonds in the reactant, resulting in a change in chemical structure and composition.

In a chemical equation, reactants are the starting materials on the left side, while products are the substances formed as a result of the reaction on the right side. The essence of a reactant's role is to provide the necessary elements or compounds that react with one another to create new substances. This transformation is fundamental to all chemical reactions, illustrating how reactants are crucial to generating products.

The other statements relate to aspects that do not accurately represent reactants. For instance, a product is formed from a reactant, so it cannot be categorized as a reactant. If a substance does not participate in the reaction, it is not considered a reactant; instead, it might be a spectator ion or a bystander that does not influence the outcome. Finally, a catalyst speeds up a reaction without being consumed or transformed in the process, which distinguishes it from a reactant, as catalysts do not undergo change in the same way that reactants do.