how to determine rate determining step in reaction mechanism.

Therate determining stepis the sloweststepof a chemical reaction thatdeterminesthe speed (rate) at which the overall reaction proceeds.
Consider an example of a reaction,
NO2(g)+CO(g)→NO(g)+CO2(g)
which occurs in two elementary steps:
NO2+NO2→NO+NO3(slow)
NO3+CO→NO2+CO2(fast)
Because the first step is the slowest step, the overall reaction cannot be proceed any faster than the rate of the first elementary step. The first elementary step in this example is therefore the rate-determining step. The rate equation for this reaction is equal to the rate constant of step 1 multiplied by the reactants of that first step. If the rate constant of step 1 is denoted k1,then the rate of the the first step in the reaction (and the total reaction) will be
rate=k1[NO2][NO2]=k1[NO2]2