Question

two versions of an element with different numbers of neutrons are called electron pairs. isotopes. ions. molecules. re - runs.

Explanation:

Isotopes are defined as two or more forms of the same element that have the same number of protons but different numbers of neutrons in their nuclei. Electron - pairs are related to bonding in atoms, ions are atoms or molecules with a net electric charge, molecules are groups of atoms held together by chemical bonds, and re - runs have no relation to this atomic concept.

Answer:

isotopes.