Define the following :
(i) Elementary step in a reaction,
(ii) Rate of the reaction.

Explanation

(i) Elementary step in a reaction : The slowest step is called rate determining step in the proposed mechanism. E.g.,
The reaction occurs in two steps :
`{:(NO_(2)+F_(2)rarr NO_(2)F+F " slow step"),(NO_(2)+F rarr BO_(2)F" fast step"),(ulbar(2NO_(2)+F_(2)rarr 2NO_(2)F " Net reaction")):}`
The rate is determined by the first step which is the slower of the two step. Each of the step is called elementary reaction.
(ii) The rate of a chemical reaction at a given temperature may depend on the concentration of one or more reactants and products. The representation of rate of reaction in terms of concentration of reactants is known as rate law.