What property describes how matter reacts when it undergoes a chemical change?

The property that describes how matter reacts when it undergoes a chemical change is indeed a chemical property. Chemical properties are characteristics of a substance that become evident during a chemical reaction. They describe the behavior of a substance in the context of its ability to undergo specific chemical changes or reactions. For example, the ability of iron to rust when exposed to oxygen and moisture is a chemical property.

In contrast, physical changes (the first option) involve changes to the form or appearance of a substance without altering its chemical composition, such as melting or boiling. Density refers to the mass of a substance per unit volume and is a physical property rather than a chemical one. Phase changes (the last option), like transitioning from solid to liquid, also do not involve changes in the chemical structure of substances; they are physical changes associated with temperature and pressure variations.