Question

What is a mass number (A)?

Answer 1

The mass number, also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. It is approximately equal to the atomic mass of the atom expressed in atomic mass units.

Answer 2

The mass number in a nucleus is the combined number of protons and neutrons, so it's protons and neutrons, and A symbolizes it. So A is the number of masses, which is equal to the number of protons, that is the number of atoms that we symbolized by Z, plus the number of neutrons.