Physical changes
a. are only caused through burning a material
b. cannot be detected by the naked eye
c. do not change the identity of the substance
d. change the identity of a substance

C. Physical changes do not change the identity of a substance, only the physical appearance such as shape or form. If you break a pencil in half, it is still composed of the same material and therefore keeps its identity as the substance it was before the physical change. Phase changes, such as ice melting, is also a physical change because it changes form. But ice is still made of H20 just like water and steam are comprised of H20.