Suppose we have 12 protons and 12 neutrons. We can assemble them to form either a 24Mg nucleus or two 12C nuclei. In which of the two cases more energy will be liberated?
If we assemble 6 protons and 6 neutrons to form 12C nucleus, 92.15 MeV (product of mass number and binding energy per nucleon of carbon-12) of energy is released. Therefore, the energy released in the formation of two carbon nuclei is 184.3 MeV. On the other hand, when 12 protons and 12 neutrons are combined to form a 24Mg atom, 198.25 MeV of energy (binding energy) is released. Hence, in case of 24Mg nucleus, more energy is liberated.