Exam-style question
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A certain radioactive isotope has a half-life of 5 years. If you start with 80 grams of this isotope, how much will remain after 15 years?.
Model answer
What a good answer should say
- After 15 years, 10 grams of the isotope will remain.
Explanation
Why this works
This question assesses the ability to apply the concept of half-life. After 15 years, which is three half-lives (5 years each), the amount of isotope is halved three times: 80g → 40g → 20g → 10g.
Common mistake
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