Which is considered a physical property of matter?

Solubility is indeed considered a physical property of matter because it describes the ability of a substance (the solute) to dissolve in a solvent to form a solution. This property is observable and can be determined without changing the chemical composition of the substance itself. For instance, when salt dissolves in water, it retains its chemical identity; the process is reversible, and the salt can be recovered.

In contrast, reactivity, flammability, and radioactivity are classified as chemical properties. This means they pertain to how a substance interacts with other substances and involve changes in chemical composition. Reactivity refers to how readily a substance will undergo a chemical reaction, flammability is the ability to ignite and burn, while radioactivity involves the emission of radiation as unstable isotopes decay into more stable forms. These properties reflect transformations that alter the chemical structure of the matter involved, distinguishing them from the more straightforward, identity-preserving characteristics defined by physical properties like solubility.