Which term refers to a version of an element with slightly different atomic masses?

• A. Element
• B. Mass Number
• C. Isotope
• D. Atom

Answer: (C)

Isotopes. Atoms of the same element can come in different forms that differ in the number of neutrons, which changes their atomic mass. Protons define the element, so all isotopes share the same element identity, but the neutron count varies, giving mass variations. For example, carbon-12 and carbon-14 are both carbon because they have the same number of protons, but carbon-12 has fewer neutrons than carbon-14, so their masses differ. The mass number refers to the total count of protons and neutrons in a specific nucleus, not to the idea of a version of the element itself. The average atomic mass on the periodic table is a weighted average of these isotopes. An element is defined by its number of protons, and an atom is a single unit that can be of any isotope.