A radioactive sample contains 1200 nuclei and has a half-life of 12 days. How many undecayed nuclei remain after 36 days?
Answer and explanation
Correct answer: C. 150
- Step 1: 36 days is 3 half-lives.
- Step 2: Each half-life halves the number of nuclei: 1200 / 2^3 = 150.
Answer
150.
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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