Lucas reagent is:

Options

A. am. `Cu_2Cl_2`
B. conc. HCl + anhydrous `ZnCl_2`
C. `NaNO_2`+ dil HCl
D. acidified `KMnO_4`

Answer

**Step-by-Step Solution:**

1. **Understanding Lucas Reagent**: Lucas reagent is used for the identification of alcohols. It is a mixture of concentrated hydrochloric acid (HCl) and anhydrous zinc chloride (ZnCl₂).

2. **Composition of Lucas Reagent**: The reagent is prepared by mixing equimolar concentrations of concentrated HCl and anhydrous ZnCl₂. Anhydrous means that the zinc chloride does not contain any water of crystallization.

3. **Purpose of Lucas Reagent**: The primary purpose of Lucas reagent is to differentiate between primary, secondary, and tertiary alcohols based on their reactivity.

4. **Reaction with Alcohols**: When Lucas reagent is added to alcohols, all types (primary, secondary, and tertiary) will initially produce turbidity. However, the rate of turbidity formation varies among the types of alcohols.

5. **Rate of Reaction**: Tertiary alcohols react the fastest with Lucas reagent, followed by secondary alcohols, and primary alcohols react the slowest. This is due to the stability of the carbocations formed during the reaction, where tertiary carbocations are the most stable.

6. **Mechanism of Reaction**: The reactions of alcohols with Lucas reagent follow the SN1 mechanism. The formation of the carbocation intermediate is crucial for the reaction to proceed.

7. **Conclusion**: Based on the above points, the correct identification of Lucas reagent is that it is a mixture of concentrated hydrochloric acid and anhydrous zinc chloride.

**Final Answer**: Lucas reagent is a mixture of concentrated hydrochloric acid (HCl) and anhydrous zinc chloride (ZnCl₂).

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