Which statement best describes chemical properties of matter?

A: Chemical properties, such as density, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure.
B: Chemical properties, such as reactivity, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure.
C: Chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form.
D: Chemical properties, such as boiling point, are generally observed as the identity of a substance changes and one or more new substances form.

for e d g e n u i t y ppl its: C: Chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form.