Concentration of the reactant in first-order is reduced to $\frac{1}{e^2}$  after : $\left(\text{ Natural life }=\frac{1}{k}\right)$

Here,

$$\begin{gathered} k\times \frac{n}{k}=\ln \left[\frac{C_0}{\frac{C_0}{e^2}}\right] \\ n=\ln \left[{\mathrm{e}}^2\right] \\ \mathrm{n}=2 \end{gathered}$$

Thus, concentration of the reactant in first-order is reduced to $\frac{1}{e^2}$ after two natural life-time