A radioactive sample contains 1600 nuclei and has a half-life of 8 days. How many undecayed nuclei remain after 24 days?
Answer and explanation
Correct answer: A. 200
- Step 1: 24 days is 3 half-lives.
- Step 2: Each half-life halves the number of nuclei: 1600 / 2^3 = 200.
Answer
200.
Why not the others: Decay is exponential: the number is halved each half-life, not reduced by a fixed amount; using one half-life too few leaves too many nuclei.
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