IB · E · multiple choice
Nuclear and quantum physics · Question 3
Nuclear and quantum physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.
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multiple choice1 mark
A sample contains 8.0 × 10²⁰ nuclei of a radioactive isotope with a half-life of 12 days. How many nuclei remain undecayed after 36 days?
- A
1.0 × 10²⁰
- B
2.0 × 10²⁰
- C
2.7 × 10²⁰
- D
4.0 × 10²⁰
Ready to self-mark?Reveal the detailed answer guide
Answer overviewCorrect answer: A — 1.0 × 10²⁰
01
1 markAnswer and reasoning
How to approach it
Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.
- 1
The correct choice is A: 1.0 × 10²⁰
- 2
36 days is three half-lives, so the number is halved three times: 8.0 → 4.0 → 2.0 → 1.0. C divides by three, which is the answer of a candidate treating decay as linear.
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