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⚛️ Physics  ·  Nuclei  ·  NEET & JEE

In a nuclear reaction, which of these is NOT conserved?

Answer: Kinetic energy.

  • A Mass number
  • B Charge
  • C Kinetic energy
  • D Mass-energy (total)

Correct answer: C. Kinetic energy

Explanation: Kinetic energy alone is not conserved in nuclear reactions (some converts to binding energy). Mass-energy (total) is conserved.

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.

Read the full Nuclei notes →