Here's why:

* Physical properties can be observed or measured without changing the chemical composition of the substance. Odor is a sensory perception that arises from the interaction of molecules with our olfactory system. It doesn't change the substance itself.

* Chemical properties describe how a substance reacts with other substances or how it changes its chemical composition.

For example, if we were to talk about the flammability of a gas (whether it burns), that would be a chemical property, as the gas undergoes a chemical change when it burns.