JEE Main 31-Aug-2021 Shift 1 Solved Paper

According to given question, the decay is as shown below
A

→

λA

B

→

λB

C(Stable)
Let N0 be the original number of atoms in the radioactive nucleus A.
Initially at t = 0,
Number of atoms of B in the sample is zero.
According to radioactive decay law,
i.e. N=N0e−λt ...(i)
With the increase in time t , the number of atoms of B will start increasing and reaches a maximum value.
After reaching the maximum value, B will start decaying into C.
Since, number of atoms varies with time following an exponential law i.e. Eq. (i).
So, the graph between number of atoms and t will be exponential in nature. Thus, the correct option is (b).