Consider a homogeneous reaction occurring in a bulk liquid, $AB.$ The concentration of $A$ is $C_A,$ and the reaction rate constant is $k_f.$ What is the average lifetime of $A?$ Note that lifetime is defined as the time during which a species stays intact, before transforming into another chemical species.

$2$a$)$ Now consider an electrochemical reaction, $O+e^{-}R.$ The concentration of $O$ at the electrode surface is $C{o}_o,$ the electrode surface area is $A,$ and the reaction rate constant is $k_f.$ Assume that the charge transfer process can only occur within a small distance $($tunneling distance$)$ d from the electrode surface. For the $O$ species within this distance d from the electrode surface, what is their average lifetime?

$2$b$)$ For the same electrochemical reaction, $O+e^{-}R,$ assume $C_O=1M,d=1nm,A=1c{m}^2,$ and $k{f}_f$ is within the range of ${10}^{-9}-10c\frac{m}{s}.$ What is the range of lifetime for the species $O$ within the charge transfer distance from the electrode surface?