Define the following form :
Atomic mass number
It is the sum of total number of protons and neutrons present in a nucleus.
atomic mass number = number of protons + number of neutrons.
Atomic number = number of protons = number of electrons.It is denoted by Z.
Mass number = number of protons + number of neutrons. It is denoted by A.
For example : Carbon atom its, Number of proton = 6
Number of neutrons = 6
Number of electron = 6
Atomic number (Z) = number of protons = number of electrons = 6
Mass number (A) = number of proton + number of neutrons = 6 + 6 =12