the unit of zero order rate constant is what?

concentration/time

See
http://en.wikipedia.org/wiki/Rate_equation#Zero-order_reactions

In order to determine the unit of the zero order rate constant, let's first understand what zero order kinetics refers to.

In chemical kinetics, zero order refers to a reaction where the rate of the reaction is independent of the concentration of the reactants. This means that the rate of the reaction does not change even if the concentration of the reactants is changed.

For a zero order reaction:

Rate = k

Where:
Rate: Rate of the reaction
k: Zero order rate constant

To determine the unit of the zero order rate constant (k), we need to inspect the rate equation for the reaction. The unit of the rate will depend on the units of the reactants involved.

For example, if the rate is given in moles per liter per second (mol/L/s), the unit of the zero order rate constant (k) will be in units of moles per liter per second (mol/L/s) as well.

The unit of the zero order rate constant can vary depending on the specific reaction being studied and the units used to express the rate of the reaction. It is important to remember that the units of the rate constant will always be consistent with the units used to express the rate of the reaction.

Therefore, without further information about the specific reaction and the units used to express the rate, I cannot provide a definitive answer to the unit of the zero order rate constant.