Answer: At short range (< 2-3 fm), between any nucleons.
- A Between protons only, with no effect on neutrons at all
- B At long range, extending across the entire size of an atom
- C At short range (< 2-3 fm), between any nucleons
- D Between nucleons and electrons, mediating their mutual attraction
Correct answer: C. At short range (< 2-3 fm), between any nucleons
Explanation: Strong force (residual from QCD): short range (~1-3 fm), attractive at ~1-3 fm, repulsive below ~0.7 fm. Holds nucleus together against Coulomb repulsion.
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.