Explain `SN^(2)` reaction

Explanation

`SN^(2) `: Substitution nucleophilic bimolecular reaction : In this reaction the rate of reaction depends on the concentration of alkyl halide and also on the concentration of nucleophile hence it is a bimolecular reaction .

The order of reactivity of alkyl halides towards `SN^(2)` reaction .
`CH_(3)- X gt` Primary halide `gt` Secondary halide `gt` Tertiary halide .
For a given alkyl group , the reaction of the alkyl halide , R- X follows the same order in both the mechanism `R - I gt R - Br gt R-Cl gt R - F`