Which of the following alkyl halides is most reactive towards ${\text{S}}_{\text{N}}2$ reaction?

Solution

1. The ${\text{S}}_{\text{N}}2$ reaction mechanism involves a backside attack by the nucleophile.
2. Steric hindrance significantly slows down the rate of ${\text{S}}_{\text{N}}2$ reactions.
3. Methyl chloride has the least steric hindrance among the given options.
4. Hence the answer is (A).