At time t =0, a material is composed of two radioactive atoms A and B, where N_A (0)=2 N_B (0). The decay constant of both kind of radioactive atoms…

At time $\displaystyle \mathrm{t}=0$, a material is composed of two radioactive atoms A and B, where $\displaystyle \mathrm{N}_{\mathrm{A}}(0)=2 \mathrm{~N}_{\mathrm{B}}(0)$. The decay constant of both kind of radioactive atoms is $\displaystyle \lambda$. However, A disintegrates to B and B disintegrates to C. Which of the following figures represents the evolution of $\displaystyle \mathrm{N}_{\mathrm{B}}(\mathrm{t}) / \mathrm{N}_{\mathrm{B}}(0)$ with respect to time t ? $$\left[\begin{array}{l} \mathrm{N}_{\mathrm{A}}(0)=\text { No. of A atoms at } \mathrm{t}=0 \\ \mathrm{~N}_{\mathrm{B}}(0)=\text { No. of B atoms at } \mathrm{t}=0 \end{array}\right] $$