Answer: Iron (Fe-56).
- A Hydrogen
- B Iron (Fe-56)
- C Uranium
- D Helium
Correct answer: B. Iron (Fe-56)
Explanation: Iron-56 has maximum binding energy per nucleon (~8.8 MeV/nucleon). Elements lighter or heavier than iron release energy by fusion or fission respectively.
Binding energy per nucleon rises sharply for light nuclei, peaks around iron-56 (the most stable nucleus), then slowly declines for heavier nuclei - which is exactly why fusing light nuclei or splitting heavy nuclei both release energy: each moves the products toward this stability peak.
Concept context
Radioactivity, nuclear reactions, fission, fusion, and binding energy.