Define ‘order of a reaction’.

The Order of a reaction refers to the relationship between the rate of a chemical reaction and the concentration of the species taking part in it. The sum of powers of the concentrations of the reactants in the rate law expression is called the order of a reaction.

If a reaction is of second order in A and first order in B, the differential rate equation is-

Rate = = k[A][B]²

Where k is the rate constant.