Rank the species below in order of decreasing leaving group capabilities in SN2 reactions (best leaving group to worst). A. H2N-
B. CH3O-
C. C6H5SO3-
D. H2O
1. Best
2. Worst

H2O> C6H5SO3- > CH3O- > H2N-

Explanation:

SN2 reaction is a reaction in which there is a synchronous departure of the leaving group and attachment of the incoming nucleophile in the transition state. Hence, an SN2 reaction passes through a single transition state. It is a bimolecular reaction.

A good leaving groups must be stable on its own. Usually, weak bases and neutral species are good leaving groups.

The order decreasing leaving group capabilities in SN2 reactions for the species listed in the question is;

H2O>C6H5SO3-> CH3O-> H2N-

Hence H2O is the best leaving group while H2N- is the worst leaving group.