* Physical properties are characteristics that can be observed or measured without changing the substance's chemical composition. Examples include color, density, melting point, and boiling point.

* Chemical properties describe how a substance reacts with other substances or how it changes its chemical composition. Flammability describes the ability of a substance to burn in the presence of oxygen, which is a chemical reaction.

When acetone burns, it undergoes a chemical reaction with oxygen, producing carbon dioxide, water, and heat. This change in chemical composition is the defining factor that classifies flammability as a chemical property.