Answer:
See explanation
Step-by-step explanation:
A unimolecular reaction is an elementary reaction in which the rearrangement of a single molecule produces one or more molecules of product(Chem Purdue).
A bimolecular reaction refers to the chemical combination of two molecular entities in a reaction that can be considered either reversible or irreversible(Springer).
Elementary reaction refers to any reaction that takes place in a single reactive encounter.
Overall reaction is the sum of all the steps of a non-elementary reaction.