Answer: The initial amount of radioactive isotope is assumed known and decay is predictable.
- A The decay constant of the isotope changes predictably over time as generally observed
- B The initial amount of radioactive isotope is assumed known and decay is predictable
- C The daughter products formed gradually disappear from the sample in typical laboratory settings
- D All radioactive isotopes decay at exactly the same fixed rate under usual circumstances
Correct answer: B. The initial amount of radioactive isotope is assumed known and decay is predictable
Explanation: Dating: knowing initial ratio (from atmospheric C-14/C-12 for carbon dating), measuring current ratio, and knowing half-life allows calculation of elapsed time.
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.