Q 12-13-093JEE MainJEE Main 2022 (27 Jul, Shift 2)Easy
The activity of a radioactive material is $6.4\times10^{-4}$ curie. Its half life is $5$ days. The activity will become $5\times10^{-6}$ curie after
Answer: (D) $35$ days
$$\frac{A_0}{A} = \frac{6.4\times10^{-4}}{5\times10^{-6}} = 128 = 2^7$$
Seven half-lives: $t = 7\times5 = 35$ days.
Solution by Sreeraj P, M.Sc Physics