Binding Energy Per Nucleon
Looking at the binding-energy-per-nucleon curve, a student notices it peaks near a certain mass number, indicating the most stable nuclei, and is asked to identify that region.
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About This Question
- Subject
- physics
- Chapter
- atoms and nuclei
- Topic
- binding energy per nucleon
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
Mass numbers around 56, near iron
NCERT presents the binding-energy-per-nucleon curve, which plots how tightly each nucleon is held as a function of mass number. The curve rises steeply for light nuclei, reaches a broad maximum of about 8.8 MeV per nucleon near mass number 56, and then declines slowly for heavier nuclei. The peak marks the most stable nuclei, which is why nuclei near iron are the endpoint of stellar fusion. The helium region is wrong because, although helium-4 is unusually stable for a light nucleus, its per-nucleon binding of about 7 MeV is below the iron peak. The uranium region is wrong because heavy nuclei have lower per-nucleon binding and can release energy by fission. The hydrogen region is wrong because a lone proton has zero binding energy per nucleon. As stated in NCERT Class 12, Chapter 13 (Nuclei), the shape of this curve explains why fusion of light nuclei and fission of heavy nuclei both release energy. A plausibility check: energy is released only when reactions move nuclei toward the iron peak, consistent with the curve's maximum lying there.
This easy difficulty physics question is from the chapter atoms and nuclei, covering the topic of binding energy per nucleon. It appeared in the 2025 exam.
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