Question

isotopes are atoms of the same element with the same number of protons and a different number of
neutrons.
electrons.
ions.
molecules.

Explanation:

Isotopes are atoms of the same element. By definition, atoms of the same element have the same number of protons. The difference between isotopes lies in the number of neutrons. For example, carbon - 12 and carbon - 14 are isotopes of carbon. Carbon - 12 has 6 neutrons ($12 - 6$ protons) and carbon - 14 has 8 neutrons ($14 - 6$ protons). Molecules are made up of atoms. Ions are atoms or molecules with a net electric charge. Electrons are sub - atomic particles, but the key difference between isotopes is not in the number of electrons (in a neutral atom, the number of electrons equals the number of protons, and for isotopes, since the number of protons is the same, in neutral form, the number of electrons is also the same).

Answer:

neutrons