Which among \(MeX, RCH_2X, R_2CHX, R_3CX\) is most reactive towards \(S_N2\) reaction?

\(MeX\)

The answer is (4) \(MeX\).

\(S_N2\) reactions are nucleophilic substitution reactions that occur in one step. The rate of an \(S_N2\) reaction depends on the reactivity of the alkyl halide and the strength of the nucleophile. The more reactive the alkyl halide, the faster the reaction will occur.

The order of reactivity of alkyl halides towards \(S_N2\) reactions is:

• Methyl halides (1°) are the most reactive because they have the least steric hindrance.
• Primary halides (1°) are less reactive than methyl halides because they have some steric hindrance.
• Secondary halides (2°) are less reactive than primary halides because they have more steric hindrance.
• Tertiary halides (3°) are the least reactive because they have the most steric hindrance.

Therefore, methyl halides are the most reactive towards \(S_N2\) reactions.