Answer: The atomic mass number is determined only by the number of nucleons in the nucleus
Explanation:
Atomic number is defined as the number of protons or electrons that are present in a neutral atom. It is represented by the symbol 'Z'
Atomic number = number of protons = number of electrons
Mass number is defined as the sum of number of protons and neutrons that are present in an atom. It is represented by the symbol 'A'
Mass number = Number of protons + Number of neutrons
Nucleons are defined as the sub-atomic particles which are present in the nucleus of an atom. Nucleons are protons and neutrons.
Hence, the atomic mass number is determined only by the number of nucleons in the nucleus