Answer: Nuclei with closed shell structure (extra stability).
- A Isotopes with equal protons and neutrons according to standard textbooks
- B Nuclei with closed shell structure (extra stability)
- C Number of isotopes in general practice as frequently described
- D Decay products in most textbook accounts during normal conditions
Correct answer: B. Nuclei with closed shell structure (extra stability)
Explanation: Magic numbers: closed shells in nuclear shell model (analogous to noble gas electronic structure). Nuclei with magic Z or N are exceptionally stable.
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.