Chemistry Regents Practice Test 2026 - Free Chemistry Regents Practice Questions and Study Guide

Isotopes are defined as atoms of the same element that have the same number of protons but differ in the number of neutrons. This difference in neutrons results in isotopes having different atomic masses. For instance, carbon has isotopes such as carbon-12 and carbon-14, where the number indicates the total number of protons and neutrons. Since isotopes retain the same chemical properties, they are recognized as variants of the same element, allowing for specific applications in fields like medicine, archaeology, and nuclear energy.

Other options do not accurately describe isotopes. For example, atoms with the same number of electrons would encompass ions and neutral atoms, and it does not relate to isotopes specifically. Atoms of different elements with identical mass describes an entirely different concept known as isobars. Finally, varying atomic numbers refers to different elements rather than variations within a single element. Thus, the accurate definition of isotopes aligns with the statement that describes atoms of the same element with different numbers of neutrons.