American Registry of Radiologic Technologists (ARRT) Practice Exam 2025 - Free Radiologic Technologist Practice Questions and Study Guide

The term that describes nuclei with different atomic numbers but the same mass is "isobars." Isobars are atoms or nuclei that have the same mass number, which is the sum of protons and neutrons, but differ in their number of protons, resulting in different atomic numbers. This distinction means that isobars represent different elements in the periodic table, even though they have the same total number of nucleons.

In contrast, the other terms refer to different nuclear configurations. Isotopes are nuclei of the same element that have the same number of protons but different numbers of neutrons, leading to variations in mass. Isomers are nuclei that have the same number of protons and neutrons but exist in different energy states. Isotones refer to nuclei that have the same number of neutrons but different numbers of protons and thus different atomic numbers. Each of these terms highlights different relationships among atomic structure and nuclear composition, but isobars specifically pertain to differing atomic numbers with identical mass numbers.