Q 12-13-099JEE MainJEE Main 2021 (31 Aug, Shift 1)Easy
A sample of a radioactive nucleus $A$ disintegrates to another radioactive nucleus $B$, which in turn disintegrates to some other stable nucleus $C$. Plot of a graph showing the variation of number of atoms of nucleus $B$ versus time is: (Assume that at $t = 0$, there are no $B$ atoms in the sample)
Answer: (C) see figure
Initially $N_B = 0$. As $A$ decays, $B$ builds up, so $N_B$ rises from zero.
As $A$ is used up, the decay of $B$ dominates and $N_B$ falls smoothly towards zero, since the final product $C$ is stable.
So $N_B$ rises smoothly from zero to a maximum and then decays, which is graph (3).
Solution by Sreeraj P, M.Sc Physics