It is used to distinguish between primary, secondary, and tertiary alcohol:

Explanation

Lucas reagent, a mixture of concentrated hydrochloric acid (HCl) and zinc chloride (ZnCl₂), is primarily used to distinguish between primary, secondary, and tertiary alcohols through a process known as the Lucas test. When an alcohol is treated with Lucas reagent, the reaction proceeds via the formation of an alkyl chloride. Tertiary alcohols react rapidly, often within minutes, to form insoluble alkyl chlorides, leading to an immediate cloudiness. Secondary alcohols take longer, while primary alcohols react very slowly, if at all, under these conditions. This differential reactivity helps in identifying the alcohol type based on the time taken for the reaction to occur.