Answer: ²³⁴Th.
- A ²³⁴Th
- B ²³²Th
- C ²³⁴Pa
- D ²³⁶U
Correct answer: A. ²³⁴Th
Explanation: Alpha emission: Z decreases by 2, A decreases by 4. U-238 (Z=92) → Th-234 (Z=90, A=234).
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.