Q 12-13-129JEE MainJEE Main 2019 (12 Apr, Shift 2)Easy
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:
Answer: (D) $9 : 8$
After $60$ min, A has gone through 6 half-lives and B through 3:
$$\frac{N_0\left(1 - \frac1{64}\right)}{N_0\left(1 - \frac18\right)} = \frac{63/64}{56/64} = \frac98$$
Solution by Sreeraj P, M.Sc Physics