Answer: The mass number of an element tells us about the number of particles present in the nucleus of an atom
Step-by-step explanation:
Nucleons are defined as the sub-atomic particles which are present in the nucleus of an atom. Nucleons are protons and neutrons.
Atomic number is defined as the number of protons or electrons that are present in a neutral atom.
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.
Mass number = Number of protons + Number of neutrons
For Example: Taking an isotope of chlorine, Cl-35
Atomic number = Number of protons = 17
Mass number = Nucleons = 35
Hence, the mass number of an element tells us about the number of particles present in the nucleus of an atom