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JEE Main 2019 (12 Apr, Shift 2) · Law of Radioactive Decay

Law of Radioactive Decay question from JEE Main 2019 (12 Apr, Shift 2)

Q80JEE Main 2019 · 12 APR · SHIFT 2Medium

Law of Radioactive Decay

Half lives of two radioactive nuclei A and B are 10 minutes and 20 minutes, respectively, If initially a sample has equal number of nuclei, then after 60 minutes, the ratio of decayed numbers of nuclei A and B will be:

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Answer: (a)

In 60 min: A goes through 6 half-lives, B through 3.
Decayed A $= N_0(1 - \frac{1}{64}) = \frac{63}{64}N_0$ ; decayed B $= N_0(1 - \frac{1}{8}) = \frac{56}{64}N_0$ .
Ratio $= 63 : 56 = 9 : 8$ .
So the answer is (a) 9 : 8.

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