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Counting What Remains After Two Decays 4 questions
Counting What Remains After Two Decays
Base your answers on the information provided and your knowledge of chemistry. Use the 2025 Chemistry Reference Tables as needed.
A classroom simulation contains two radioactive parents, P and Q. Each decay makes one nucleus of the same stable daughter type. There are no daughter nuclei initially. Over one model interval half the P parents decay, while one quarter of the Q parents decay.
| Record after one interval | Count |
|---|---|
| P parents still present | 20 |
| Q parents still present | 30 |
| Stable daughters in all | 30 |
Question 1
Which number of P parents must have been present at the start?
- 20
- 30
- 40
- 50
Question 2
Calculate the starting number of Q parents and the number of daughters made by Q.
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Question 3
A student adds all 30 daughters to the 20 remaining P parents to infer the original P count. Evaluate the calculation using both parent records.
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A repeat display hides both parent counts and reports only the 30 pooled daughters. The starting amounts of the two parents are not given.
Question 4
Give two possible pairs of P and Q decay counts consistent with the 30 pooled daughters. Explain why the reading cannot distinguish the pairs.
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