Explain how units can be used to guide calculations in the four steps used in solving stoichiometric
problems.

the answer is b & c i believe : )

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

you need to have a picture of the atom that way we can answer it