Answer: Mediating the nuclear force (residual strong force).
- A Mediating the weak interaction responsible for beta decay
- B Mediating the nuclear force (residual strong force)
- C Mediating the electron capture process within the nucleus
- D Causing spontaneous radioactivity in unstable nuclei generally
Correct answer: B. Mediating the nuclear force (residual strong force)
Explanation: Yukawa (1935): nuclear force mediated by pion exchange. Heavier mediator (compared to photon) gives short range. Pion mass ~ 140 MeV.
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.