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NEET 1998 (AIPMT) · Law of Radioactive Decay

Law of Radioactive Decay question from NEET 1998 (AIPMT)

Q121NEET 1998 · AIPMTMedium

Law of Radioactive Decay

Half-lives of two radioactive substances $A$ and $B$ are respectively $20\text{ min}$ and $40\text{ min}$ . Initially the samples of $A$ and $B$ have equal number of nuclei. After $80\text{ min}$ the ratio of remaining number of $A$ and $B$ nuclei is

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Answer: (c)

In 80 min: A completes $80/20 = 4$ half-lives, B completes $80/40 = 2$ half-lives.
$N_A = N_0/16$ , $N_B = N_0/4$ .
$N_A : N_B = 1 : 4$ , so the answer is (c).

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