Question detail
If a radioactive substance has a half-life of 5 years, how much of a 100g sample remains after 15 years?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Atoms and nuclear radiation
Question
- A. 100g
- B. 50g
- C. 25g
- D. 12.5g
Answer
12.5g
Explanation
After 15 years (which is three half-lives), the sample would reduce to 100g -> 50g -> 25g -> 12.5g.
Common mistake
Misunderstanding Half-Life Effects
Students often confuse the concept of half-life with the total decay time, thinking that a shorter half-life means the substance will completely decay faster than it actually does.
Emphasize that half-life is the time taken for half of the radioactive nuclei to decay, and that multiple half-lives are required for a substance to decay significantly.
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