A primary alkyl halide would prefer to undergo _____________. (i) SN1 reaction (ii) SN2 reaction (iii) α–Elimination (iv) Racemisation

Option (ii) is the answer.

Primary alkyl halides undergo SN​2 mechanisms because 1∘ substrates have little steric hindrance to nucleophilic attack and 1∘ carbocations are relatively unstable. Because primary alkyl halides are the least sterically hindered among the primary, secondary, and tertiary alkyl halides, they undergo the $SN_2$ reaction.