Question

isotopes are two atoms that have the same ____ but different ____. a mass number, atomic number b number of protons, number of neutrons c number of neutrons, number of protons d number of protons, number of electrons

Explanation:

Isotopes are atoms of the same element with the same number of protons (atomic number) but different numbers of neutrons (and thus different mass - numbers).

Answer:

A. mass number; atomic number