Answer: Electrostatic energy exceeds surface energy (fissility parameter x > 1 approx).
- A A < 50, a mass number range where stable light nuclei are common
- B Electrostatic energy exceeds surface energy (fissility parameter x > 1 approx)
- C A = 56, the mass number of the most stable nucleus, iron-56
- D Temperature exceeds 10⁹ K, a condition relevant to stellar fusion instead
Correct answer: B. Electrostatic energy exceeds surface energy (fissility parameter x > 1 approx)
Explanation: Liquid drop: fission favorable when deformation energy cost (surface) < energy gain (Coulomb reduction). Fissility x = E<sub>C</sub>/(2E<sub>S</sub>) > 1 means spontaneous fission possible.
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.