Order of a reaction: Order of a reaction is defined as the sum of the powers of the concentration terms appearing in the experimentally observed rate law. 0 and 1 are possible values.
Molecularity: The minimum number of molecules, atoms or ions of reactants required for an elementary reaction to occur is indicated by the sum of the stoichiometric coefficients of the reactant(s) in the chemical equation, is known as molecularity of the reaction. 1 and 2 are possible values.
The dissociation of H2O2(aq) is a first order reaction and H2(g)+Cl2(g)hv−→2HCl is a zero order reaction.