For reaction a A→x P, when [A] = 2.2 mM, the rate was found to be 2.4 mM s−1. On reducing concentration of A to half, the rate changes to 0.6 mM s−1. The order of reaction with respect to A is

aA→xPRate of reaction =[A]aOrder of reaction = a[A]1=2.2 mM, r1=2.4 mM s−1 ...... (i)[A]2=2.2/2 mM, r2=0.6 mM s−1 or, 2.44 .....(ii)On reducing the concentration of A to half, the rate of reaction is decreased by four times. Rate of reaction =[A]2Order of reaction = 2.