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MHT CET 2021 (24 Sep, Shift 2) · Law of Radioactive Decay

Law of Radioactive Decay question from MHT CET 2021 (24 Sep, Shift 2)

Q56MHT CET 2021 · 24 SEP · SHIFT 2Medium

Law of Radioactive Decay

The half life of a radioactive substance is 30 minute. The time taken between 40% decay and 85% decay of the same radioactive substance is

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Answer: (c)

40% decay leaves 60%; 85% decay leaves 15%.
$\frac{60}{15} = 4 = 2^2$ , so the time gap is 2 half-lives.
$\Delta t = 2\times30 = 60$ min, so the answer is (c) 60 minute.

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