How does binding energy per nucleon vary with mass number?

Binding energy is a measure of the stability of the nucleus. Binding energy first increases with mass number and then decreases. Binding energy for nuclei with low mass number is less and gradually increases with increase in mass number. It reaches to peak at around mass number of 50. Iron nucleus (FE 56) is having almost the maximum binding energy. After that(Mass number greater than 60), the binding energy per nucleon gradually decreases.

The nucleus inside an atom consists of positively-charged  protons  and neutrally-charged  neutrons. a  proton  is a subatomic particle with a positive electric charge. allprotons  are identical.