Lucas reagent (anhydrous $ ZnC{{l}_{2}}+conc.\,HCl $ ) is used to distinguish between primary, secondary and tertiary alcohols. It reacts with $ 3{}^\circ $ -alcohol readily giving white turbidity, with $ 2{}^\circ $ -alcohol it gives turbidity after 1-2 minutes. While with $ 1{}^\circ $ -alcohol, it reacts only on heating. Hence, it will react with 2-methyl propanal-2-ol fastest. $ \underset{\text{2-}\,\text{methyl}\,\text{propanol-2}}{\mathop{C{{H}_{3}}--\underset{C{{H}_{3}}}{\overset{C{{H}_{3}}}{\mathop{\underset{|}{\overset{|}{\mathop{C}}}\,}}}\,--OH}}\,\xrightarrow{ZnC{{l}_{2}}/conc.\,HCl} $ $ \underset{\text{white}\,\,\text{turbidity}\,\text{(immediately)}}{\mathop{C{{H}_{3}}--\underset{C{{H}_{3}}}{\overset{C{{H}_{3}}}{\mathop{\underset{|}{\overset{|}{\mathop{C}}}\,}}}\,--Cl+{{H}_{2}}O}}\, $