Final answer:
For toluene, flammability is most likely a chemical property, as it describes its ability to undergo a chemical reaction – specifically combustion. Melting point, boiling point, and density are physical properties and do not involve changes in chemical composition.
Step-by-step explanation:
When discussing the chemical properties of a substance, we refer to its inherent capabilities to undergo changes that alter its identity during chemical reactions. In the case of toluene, which is also known by its chemical formula C6H5-CH3, one of its key chemical properties is its flammability. Toluene's ability to ignite and burn when exposed to an open flame or sufficient heat is a clear demonstration of a chemical property, as it involves a chemical reaction where the toluene molecule reacts with oxygen to produce carbon dioxide, water, and heat.
Other options such as melting point, boiling point, and density are considered physical properties of a substance since they describe the physical characteristics of a substance without leading to a change in its chemical composition.