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JEE Main 2021 (25 Feb, Shift 1) · Law of Radioactive Decay

Law of Radioactive Decay question from JEE Main 2021 (25 Feb, Shift 1)

Q68JEE Main 2021 · 25 FEB · SHIFT 1Medium

Law of Radioactive Decay

Two radioactive substances X and Y originally have N1 and N2 nuclei respectively. Half life of X is half of the half life of Y. After three half lives of Y, number of nuclei of both are equal. The ratio $\frac{N_1}{N_2}$ will be equal to:

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Answer: (d)

$T_X = T_Y/2$ , so in $3T_Y$ X goes through 6 half-lives and Y through 3.
$\frac{N_1}{2^6} = \frac{N_2}{2^3} \Rightarrow \frac{N_1}{N_2} = \frac{64}{8} = 8$ .
So the answer is (d) $\frac{8}{1}$ .

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