A neutral atom have equal number of protons and neutrons. In other words we can say that negative and positive charges are equal in magnitude and cancel the each other. For example if neutral atom has 6 protons than it must have 6 electrons. The number of protons or number of electrons are the atomic number of an atom while the number of protons and number of neutrons are the mass number of an atom. Every atom consist of nucleus or a positive center. The protons and neutrons are present with in the nucleus while electrons are present out side the nucleus. All these three subatomic particles construct an atom.
Example:
In Francium the number of proton and neutron can be found by subtracting the atomic number of francium from its atomic mass. The atomic number will be the number of protons and remaining will show the total number of neutrons present in nucleus.
Atomic number is 87
Atomic mass 223
223- 87 = 136
So number of neutrons are 136 and number of protons are 87.
