Question

1. two atoms of the same element with different mass numbers are called ______.

○ isotopes
○ electrons
○ nuclei
○ neutrons

Explanation:

Isotopes are defined as atoms of the same element (same number of protons) that have different mass numbers, which arises from having different numbers of neutrons. The other options are incorrect: electrons are subatomic particles, neutrons are subatomic particles, and nuclei are the central core of atoms, none of which match the given definition.

Answer:

A. isotopes