Lucas test is used to distinguish:

Solution

Chemistry ma’am · 4 steps

Lucas test is a speed test: the more stable the carbocation, the faster the solution turns cloudy.

1. The reagent. Lucas reagent is concentrated HCl with anhydrous ZnCl₂. It turns an alcohol into an alkyl chloride: ROH + HCl →(ZnCl₂) RCl + H₂O.
2. Why cloudiness appears. Small alcohols dissolve in the reagent, but the alkyl chloride does not. When it forms, it separates as fine droplets and the solution turns turbid.
3. Why the speed differs. The reaction goes through a carbocation. Its stability follows 3° > 2° > 1°, so the time taken for turbidity tells you the class of the alcohol.

   Alcohol	Carbocation formed	Turbidity at room temperature
   Tertiary (3°)	most stable	immediately
   Secondary (2°)	less stable	within about 5 minutes
   Primary (1°)	least stable	none, only on heating

4. So. Three different responses for three classes of alcohol, so the Lucas test distinguishes 1°, 2° and 3° alcohols. The answer is (a).

The idea to keep. Lucas test means turbidity speed: tertiary at once, secondary in about 5 minutes, primary not at room temperature. The speed comes from carbocation stability.

Answer from the NTA final answer key. Solution by PrepWiser.