Question: Primary, secondary and tertiary alcohols can be distinguished by:

Step 1 (Governing Principle): [0.5 Mark]
The distinction between primary ($1^\circ$), secondary ($2^\circ$), and tertiary ($3^\circ$) alcohols is based on the reactivity of the $C-OH$ bond towards concentrated hydrochloric acid ($HCl$) in the presence of anhydrous zinc chloride ($ZnCl_2$), known as the Lucas Reagent. The reaction follows the mechanism of nucleophilic substitution ($S_N1$):

Step 2 (Step-by-Step Deduction): [0.25 Mark]
The rate of reaction depends on the stability of the carbocation intermediate formed. The reactivity order is $3^\circ > 2^\circ > 1^\circ$. The observations are as follows:

• Tertiary ($3^\circ$) alcohols: React immediately at room temperature, producing turbidity (cloudiness) instantly due to the formation of insoluble alkyl chloride.
• Secondary ($2^\circ$) alcohols: Produce turbidity within 5–10 minutes at room temperature.
• Primary ($1^\circ$) alcohols: Do not produce turbidity at room temperature; they react only upon heating.

Step 3 (Final Concluded Answer): [0.25 Mark]
Based on the differential reaction rates observed through the formation of alkyl chlorides, the correct option is (A) Lucas test.

💡 EL10 Concept Insight: Think of the Lucas test like a "reactivity race"—tertiary alcohols are so unstable that they turn into cloudy oil instantly, while primary alcohols are "lazy" and won't react unless you heat them up, making it easy to tell them apart.