Nuclear fission splits a large, unstable nucleus into two smaller nuclei (releasing energy), while nuclear fusion combines two small, light nuclei into a larger one (also releasing energy). Explain why BOTH processes can release energy despite moving mass in opposite directions (splitting vs. combining), using the concept of binding energy per nucleon.

Binding energy per nucleon peaks around iron (atomic mass ≈56), meaning nuclei near iron are the most stable per nucleon of any element — both very large nuclei (like uranium) and very small nuclei (like hydrogen) sit at LOWER binding energy per nucleon than iron does. Fission of a very large nucleus produces two medium-sized nuclei that are each closer to iron's peak stability, so binding energy per nucleon INCREASES, and the excess energy is released. Fusion of very small nuclei produces a slightly larger nucleus that is also closer to iron's peak, so binding energy per nucleon also INCREASES in that direction, releasing energy as well — the two processes approach the same stability peak from opposite starting points, both moving toward greater binding energy per nucleon rather than away from it. Claiming only fission can release energy, since fusion should require net energy input rather than releasing it, ignores that fusion of light nuclei up to around iron's mass DOES release energy, exactly why stars generate energy through fusion. Claiming binding energy per nucleon increases without bound as nuclei get heavier (rather than peaking near iron and then decreasing) misdescribes the actual, well-established shape of the binding-energy-per-nucleon curve. Claiming the two processes release energy for entirely unrelated reasons, with no shared underlying explanation, misses that a single unifying concept (movement toward peak binding energy per nucleon) explains both.