Which of the following techniques is often used in the preparation of primary alkyl halides?

The preparation of primary alkyl halides is commonly achieved through nucleophilic substitution reactions. In this process, a nucleophile — often a halide ion — attacks a carbon atom that is bonded to a leaving group, typically a more electronegative atom or group. This is especially effective for primary alkyl halides because these structures have less steric hindrance, allowing nucleophiles to freely approach and attack the electrophilic carbon atom.

In nucleophilic substitution, the reaction proceeds via either an SN1 or SN2 mechanism, with primary alkyl halides favoring the SN2 pathway due to the one-step nature of the reaction, which involves a concerted attack by the nucleophile and displacement of the leaving group. This leads to the formation of a primary alkyl halide efficiently, as primary substrates offer optimal conditions for the nucleophile's attack.

The other techniques listed — electrophilic addition, hydrogenation, and electrolysis — are not typically involved in the synthesis of primary alkyl halides. Electrophilic addition usually deals with alkenes and alkynes rather than the straightforward substitution necessary for forming alkyl halides. Hydrogenation is primarily a method for converting alkenes or alkynes into alkanes