Work Step by Step
Isotopes are forms of the same element with differing numbers of neutrons. In isotopes, the number of protons and electrons remain the same. Because the number of neutrons differ between isotopes, the mass number is also different because the mass number is the number of protons plus the number of neutrons in an atom. Therefore, option D is correct because isotopes differ in the number of neutrons they contain as well as in their mass numbers.