Which statement best describes chemical properties of matter? Chemical properties, such as density, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure. Chemical properties, such as reactivity, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure. Chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form. Chemical properties, such as boiling point, are generally observed as the identity of a substance changes and one or more new substances form.

Chemical change involves formation of new substances. Hence, the correct answer is "Chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form."

The principal thing about a chemical change is that the identity of the substance must change. The identity of the substance must change as bonds between atoms of the substance are broken and rearranged.

Combustibility is a chemical property. It is observed as a substance is transformed into its oxide giving out heat and light in the process.

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