Answer: mass number.
- A mass number
- B atomic number
- C number of neutrons
- D number of electrons
Correct answer: A. mass number
Explanation: Isobars have the same mass number A but different atomic number Z (for example, argon-40 and calcium-40).
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.