Which property of matter changes during a chemical reaction?

During a chemical reaction, the property that changes is reactiveness. Reactiveness refers to how readily a substance undergoes a chemical change when it interacts with other substances. For example, reactiveness can be observed when substances combine or break apart to form new products. This is a fundamental aspect of chemical reactions, as the properties of the reactants before the reaction differ significantly from those of the products formed after the reaction.

On the other hand, mass is a property that is conserved in a closed system during a chemical reaction, according to the law of conservation of mass. While the state or quantity of substances may change during the reaction, the total mass remains constant. Boiling point is a physical property that can remain unchanged in a reaction unless temperature conditions are altered. Odour, while it may change as new substances are formed, does not specifically characterize the fundamental nature of the substances involved in the reaction as reactiveness does. Therefore, reactiveness is the most accurate choice regarding what changes during a chemical reaction.