Which of the following reaction(s) can be used for the preparation of alkyl halides?(i) ${\text{CH}}_3{\text{CH}}_2\text{OH}+\text{HCl}\stackrel{{\text{Anhyd. ZnCl}}_2}{\to }$ (ii) ${\text{CH}}_3{\text{CH}}_2\text{OH}+\text{HCl}⟶$ (iii) $({\text{CH}}_3{)}_3\text{COH}+\text{HCl}⟶$ (iv) $({\text{CH}}_3{)}_2\text{CHOH}+\text{HCl}\stackrel{{\text{Anhyd. ZnCl}}_2}{\to }$

Primary ($1^{\circ }$) and secondary ($2^{\circ }$) alcohols require a catalyst like anhydrous ${\text{ZnCl}}_2$ (Lucas reagent) to react with $\text{HCl}$. Thus (i) and (iv) work.Tertiary ($3^{\circ }$) alcohols are highly reactive and react with conc. $\text{HCl}$ even in the absence of a catalyst. Thus (iii) works.Reaction (ii) is slow/ineffective without a catalyst.