At catalyst is a. the product of a combustion reaction b. not used up in a reaction c. one of the reactants in single-replacement reactions d. a solid product of a reaction

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

it means there are 3 atoms of oxygen