The unit of rate constant of a reaction is same as that of its rate of reaction. What is the order…

Zero order. Reason: The rate of reaction has the unit $\text{mol L}^{-1}\text{s}^{-1}$. The general unit of rate constant for an $n^{\text{th}}$ order reaction is $(\text{mol L}^{-1})^{1-n}\text{s}^{-1}$. Equating the units gives $1 - n = 1$, which yields $n = 0$ (zero order).