Binding energy per nucleon decreases with A for nuclei with the atomic mass number A>100 due to weak nuclear forces. It can. be explain as :
At short distances, the nuclear force is stronger than the Coulomb force; it can overcome the Coulomb repulsion of protons inside the nucleus. At typical nucleon separation (1.3 fm) it is a very strong attractive force (104 newtons). Beyond about 1.3 fm separation, the force exponentially dies off to zero. However, the Coulomb force between protons has a much larger range and becomes the only significant force between protons when their separation exceeds about (2.5 fm,A>100).