Answer: A Z.
- A A − Z
- B A + Z
- C 2Z − A
- D A × Z
Correct answer: A. A − Z
Explanation: Mass number A counts protons plus neutrons, and Z counts protons, so the neutron number N = A − Z.
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.