Four alcohols are shaken separately with Lucas reagent ($\mathrm{ZnCl}{}_2$ in conc. $\mathrm{HCl}$) at room temperature. Which one gives turbidity immediately?

Lucas reagent converts alcohols to alkyl chlorides by an ${\mathrm{S}}_{\mathrm{N}}1$ path, so reactivity follows carbocation stability. Only the tertiary alcohol, 2-methylpropan-2-ol, forms the stable $(\mathrm{CH}{}_3){}_3\mathrm{C}{}^{+}$ at once and the insoluble chloride makes the solution turbid immediately. The secondary alcohol takes about 5 minutes and primary alcohols show no turbidity at room temperature.