Question

isotopes are one of multiple versions of an atom with different mass numbers based on variation in the number of which of the following particles? a.) neutrons b.) protons c.) nucleus d.) electrons

Explanation:

Isotopes are atoms of the same element that have the same number of protons (which defines the element) but different numbers of neutrons. The mass number of an atom is the sum of protons and neutrons. Since protons are fixed for a given element (as they determine the element's identity), the variation in mass number among isotopes comes from the different number of neutrons. Electrons are involved in chemical bonding and do not contribute to the mass number in a significant way for this context. The nucleus is the central part of the atom containing protons and neutrons, but it is not a particle in the sense of what varies for isotopes.

Answer:

A. Neutrons