The pile of ash left after a fire burns out demonstrates what concept? a. original materials remain after a physical change. b. a chemical change forms new substances. c. physical properties are never stable. d. fire recycles most substances.

because u need two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei to form isotopes.

so since they all have the same shape? i mean maybe because m& m and reeses are both chocolates