See explanation below.
Work Step by Step
(a) Average Rate is the rate of reaction calculated for a long time interval. It is defined as the amount of change/time taken. R=Δ[A]/Δt. Instantaneous Rate is the rate calculated at any instant during the reaction. It is defined as the differential of conc.(or pressure etc.) with respect to time. R= d[A]/dt. (b) Initial rate is the reaction rate when the reaction starts, or when the reactants are in their initial full concentration. In contrast, instantaneous rate is the rate at any time t.