The mass number of a nucleus is?

The mass number of a nucleus is the sum of the number of protons and neutrons present in the nucleus. These particles, protons and neutrons, are the building blocks of the nucleus and make up its atomic mass. The mass number is an important characteristic of an atom and helps to distinguish it from other atoms of the same element. For example, two isotopes of carbon, carbon-12 and carbon-14, have different mass numbers even though they both have 6 protons. It's worth noting that the mass number is not always greater than the atomic number, but it is always greater than or equal to the atomic number. The atomic number of an atom is simply the number of protons in its nucleus, and it determines what element the atom is.