What term describes the total number of protons and neutrons in an atom's nucleus?

The total number of protons and neutrons in an atom's nucleus is referred to as the mass number. This value is significant because it gives an indication of the overall mass of the atom, reflecting the combined contributions of these two types of subatomic particles. Protons and neutrons, located in the nucleus, are much heavier than electrons, which is why the mass number is predominantly determined by their count.

The mass number helps in distinguishing between different isotopes of an element, which have the same number of protons (and thus the same atomic number) but different numbers of neutrons. Each unique combination of protons and neutrons results in a specific mass number for that isotope.

The atomic number, on the other hand, only accounts for the number of protons in an atom and is essential for identifying the element itself. Atomic weight reflects the average mass of an element's isotopes, factoring in their abundances but is not a fixed number. Lastly, the term isotope number is not commonly used in this context and can lead to confusion, as isotopes are identified primarily by their mass numbers rather than any specific "isotope number." Therefore, mass number is the correct term for the total count of protons and neutrons