There is a mass defect when measuring protons and neutrons separately than to weighing atoms.
For example: The mass of protons is 1.6726486 x 10 -27 Kg and the mass of neutrons is 1.6749544 x 10 -27 Kg so the mass of a helium atom must be 6.6952048 x 10 ^-27 kg. However, the mass of a helium atom is 6.64477 x 10 -27 Kg which is less that it should be. This is because there is some mass that converts into binding energy. This energy binds the sub-atomic particles together. It can be calculated by using E = mc².
Iron is the most stable element as show on the graph above. So smaller nuclei fuse together to form heavier elements to be more like iron.
During fusion, nucleons become tightly bounded together. The binding energy per nucleon of both the nuclei is greater than the initial nuclei, this makes the nucleons even more trapped in the nucleus when the fusion occurs. As a result, the energy released is equal to the binding energy.
Nuclear fusion only occurs if the two nuclei are combined at high speeds. This is to overcome the…