Alkyl halides are prepared from alcohol by treating with:

Options

A. `HCl+ZnCl_(2)`
B. `H_(2)SO_(4)+KI`
C. `NaCl+H_(2)SO_(4)`
D. None of these

Answer

To prepare alkyl halides from alcohol, we can use specific reagents that facilitate the substitution of the hydroxyl group (-OH) in alcohol with a halide ion (X-). Here’s a step-by-step solution to the question:

### Step-by-Step Solution:

1. **Identify the Alcohol**:
- Start with a general alcohol structure, represented as RCH2OH, where R is an alkyl group.

2. **Choose the Reagent**:
- The first option provided is HCl in the presence of ZnCl2. This is a well-known reagent for converting alcohols to alkyl halides.

3. **Protonation of Alcohol**:
- The hydroxyl group (-OH) of the alcohol can be protonated by HCl. The oxygen atom in the -OH group has lone pairs and will attack the hydrogen (H+) from HCl, forming RCH2OH2+ (an oxonium ion).

4. **Formation of Carbocation**:
- The protonated alcohol (RCH2OH2+) is unstable and can lose a water molecule (H2O), resulting in the formation of a carbocation (RCH2+).

5. **Nucleophilic Attack by Chloride Ion**:
- The chloride ion (Cl-) from HCl can now attack the carbocation (RCH2+). This results in the formation of the alkyl halide (RCH2Cl).

6. **Final Product**:
- The final product of this reaction is RCH2Cl, which is the desired alkyl halide.

### Conclusion:
- The correct reagent to prepare alkyl halides from alcohol is **HCl in the presence of ZnCl2**.