The composition of Lucas reagent is

The correct answer is Option (4) → \(1\, HCl: 1\, ZnCl_2\)

Lucas reagent is a solution of anhydrous zinc chloride in concentrated hydrochloric acid, in about equimolar amounts (one mole of \( \ce{ZnCl2} \), 136 g, dissolved in about 105 g of concentrated HCl, which contains about one mole of HCl). Zinc chloride is a Lewis acid: it bonds to the oxygen of the –OH group and makes it a better leaving group, so the alcohol is converted into an alkyl chloride:

    \( \displaystyle \ce{R-OH + HCl} \xrightarrow{\ce{ZnCl2}} \ce{R-Cl + H2O} \)

Alcohols dissolve in the reagent, but the alkyl chloride does not, so a turbidity appears. It appears at once with tertiary alcohols, within about five minutes with secondary alcohols, and not at room temperature with primary alcohols. So the composition of Lucas reagent is 1 HCl : 1 ZnCl₂.

Note: The question is from beyond the NCERT textbook.