I've been wondering, Iron has the most binding energy per nucleon amongst elements and thus realized to be the most "stable" element. Smaller or bigger elements (compared to iron) can fuse or undergo fission respectively. As they fuse or undergo fission, it becomes more stable (the product element will have more binding energy per nucleon, losing its average mass per nucleon). This surplus in binding energy per nucleon comes from the rest mass deficit of the product atoms compared to the reactants. Atomic bombs use principles in fission and fusion. So, where does the energy released for the 'explosion' come from? if it comes from the mass deficit between product and reactant, where does the energy for the increase in binding energy come from? Thank you!