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⚛️ Physics  ·  Nuclei  ·  NEET & JEE

The nucleus <sup>4</sup>He has a mass defect of 0.0304 u (1 u = 931.5 MeV). Its binding energy per nucleon is about:

Answer: 7.1 MeV.

  • A 28.3 MeV
  • B 4.7 MeV
  • C 7.1 MeV
  • D 8.8 MeV

Correct answer: C. 7.1 MeV

Explanation: Total binding energy = 0.0304 &times; 931.5 &asymp; 28.3 MeV; per nucleon = 28.3/4 &asymp; 7.1 MeV.

Binding Energy per Nucleon vs Mass NumberMass number ABE/nucleonFe-56 (peak, most stable)FUSION region (light → medium)FISSION region (heavy → medium)Both processes release energy by moving nuclei toward the Fe-56 peak

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.

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