The rate of a reaction (how fast it proceeds) may depend on the concentration of various species involved in the reaction. It may depend on the concentration of one species i.e. [A] or two species, i.e. [A]² or [A][B] etc.

A rate law that is first-order overall indicates that the indices (powers) of all the species add up to a total of 1. Which of the following is an overall first-order rate law? Note: [A] = concentration of A and k is a rate constant.