Which of the following best describes the total number of neutrons and protons in the nucleus of an atom?

The total number of neutrons and protons in the nucleus of an atom is best described by atomic mass. This term refers to the combined mass of these particles, as both protons and neutrons contribute significantly to the overall mass of an atom. In practice, the atomic mass is approximately equal to the atomic number (the number of protons) plus the number of neutrons, since protons and neutrons have similar mass and are much more massive than electrons.

While atomic weight, atomic structure, and atomic number are all related concepts in atomic theory, they do not accurately describe the total number of neutrons and protons. Atomic weight refers to the average mass of an atom based on the relative abundance of its isotopes, atomic structure refers more broadly to the arrangement of electrons and the nucleus, and atomic number specifically counts the number of protons, not neutrons. Thus, atomic mass is the correct term for representing the total count of protons and neutrons in the nucleus.