What example best illustrates a physical property?

A physical property is a characteristic of a substance that can be observed or measured without changing the substance's chemical identity. The melting point is an excellent example of a physical property because it describes the temperature at which a solid transitions to a liquid, while the chemical structure of the substance remains unchanged.

In contrast, flammability, reactivity, and toxicity are classified as chemical properties. These properties involve a substance's ability to undergo a chemical change or reaction. Flammability refers to the ability of a substance to catch fire and combust, reactivity pertains to how a substance interacts with other substances to form new compounds, and toxicity involves the potential to cause harm or adverse effects through chemical interaction. These properties cannot be assessed without altering the chemical nature of the substance, which distinguishes them from physical properties like melting point.