Which of the following is not a physical property of matter?

Reactivity is not considered a physical property of matter because it describes how a substance interacts with other substances, particularly in chemical reactions. Physical properties are characteristics that can be observed or measured without changing the substance's chemical identity. These include density, color, and shape.

Density refers to how much mass is contained in a given volume, and color describes the appearance of the substance, both of which can be assessed without altering the material itself. Shape is related to the physical form and structure an object takes, which also can be examined externally without engaging in any chemical change. In contrast, reactivity involves the potential for a substance to undergo a chemical transformation when it reacts with something else, thereby changing its chemical structure and properties.