The first order liquid phase reaction $A \rightarrow P$ is conducted isothermally in a plug flow reactor of $5$ liter volume. The inlet volumetric flow rate is $1$ liter/min and the inlet concentration of $A$ is $2$ mole/liter.

If the exit concentration of $A$ is $0.5$ mole/liter, then the rate constant, in $\text{min}^{-1}$, is

1. $0.06$
2. $0.28$
3. $0.42$
4. $0.64$