Remember that :
Number of protons = Atomic number
Number of protons = Number of electrons.
Number of neutrons = Mass number - Atomic number
In order to find the number of protons and neutrons
Let us consider a Element Oxygen.
We know that atomic number of Oxygen is 8.
Atomic number = 8
Also atomic mass of oxygen is 16.
In the case of oxygen.
Atomic number is 8. Therefore, number of protons will also be 8.
Let's calculate the Number of neutrons
Number of neutrons = Mass number - Atomic number.
Number of neutrons = 16 - 8 = 8