Q 12-13-094JEE MainJEE Main 2022 (28 Jul, Shift 1)Easy
The half life period of a radioactive substance is $60$ days. The time taken for $\dfrac78$th of its original mass to disintegrate will be :
Answer: (C) 180 days
If $\dfrac78$ disintegrates, $\dfrac18 = \left(\dfrac12\right)^3$ remains: three half-lives.
$$t = 3\times60 = 180\ \text{days}$$
Solution by Sreeraj P, M.Sc Physics