Answer: Same A and Z but different energy states (metastable excited states).
- A Same A and Z but different binding energy, with no excited-state distinction
- B Same A and Z but different energy states (metastable excited states)
- C Different Z but same A, which instead describes isobars
- D Different A but same Z, which instead describes isotopes
Correct answer: B. Same A and Z but different energy states (metastable excited states)
Explanation: Nuclear isomers: same nucleus (same Z, same A) but in different long-lived excited states. Decay by gamma emission. Example: Tc-99m.
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.