Answer: 8 10 3 Bq.
- A 3.2×10<sup>4</sup> Bq
- B 1.6×10<sup>4</sup> Bq
- C 8×10<sup>3</sup> Bq
- D 2×10<sup>4</sup> Bq
Correct answer: C. 8×10<sup>3</sup> Bq
Explanation: 9 hours = 3 half-lives, so activity = 6.4 × 10<sup>4</sup>/2<sup>3</sup> = 6.4 × 10<sup>4</sup>/8 = 8 × 10<sup>3</sup> Bq.
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.