The process of converting alkyl halides into alcohols involves

I. Addition reaction

II. Substitution reaction 

III. Dehydrohalogenation reaction 

IV. Rearrangement reaction 

This is a multiple choice answer as classified in NCERT Exemplar

(II) Substitution reaction 

Alkyl halides undergo substitution reactions to form corresponding alcohol.The halide ion, X^- is substituted by OH^- ion  to form alcohol by nucleophilic substitution reaction.

R-X → R-OH