A reaction involving two different reactants can never be
Second order reaction
Bimolecular reaction
Unimolecular reaction
First order reaction
The order of the reaction does not depend on the types of molecules that react. The order of the reaction can be found out experimentally by calculations, but it is clear that the reaction can be of first order or second order.
Unimolecular reaction is a reaction in which only one type of molecule can react. But, in a reaction in which two different reactants are reacting, it cannot be a unimolecular reaction.
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