Question

explain b.e./ nucleon graph with respect to the stability of nucleus​

Answer 1

The heavier the nucleus, the greater the internal repulsive forces due to the greater number of protons and less energy must be applied to remove a nucleon from the nucleus, hence the binding energy is lower. Thus for lighter nuclei binding energy is more. The greater the binding energy, the more stable the nucleus is.

Answer 2

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N = Z is a straight line for proton numbers(Z) up to 20. The line curves upwards for all nuclei with Z>20, and the stable nuclei have more neutrons than protons.