Which of the following reaction`(s)` can be used for the preparation of alkyl halides?
(I) `CH_(3)CH_(2)OH+HCloverset(anhy.ZnCl_(2))(rarr)`
(II) `CH_(3)CH_(2)OH+HClrarr`
(III) `(CH_(3))_(3)COH+HClrarr`
(IV) `(CH_(3))_(2)CHOH+HCloverset(anhy.ZnCl_(2))(rarr)`

Options

A. (IV ) only
B. (III) and (IV) only
C. (I), (III) and (IV) only
D. (I), and (II) only

Answer

To determine which of the given reactions can be used for the preparation of alkyl halides, we need to analyze each reaction based on the type of alcohol and the conditions provided.

### Step-by-Step Solution:

1. **Reaction I: `CH₃CH₂OH + HCl (anhy. ZnCl₂) →`**
- This is a primary alcohol (ethanol) reacting with HCl in the presence of anhydrous ZnCl₂.
- The presence of ZnCl₂ helps in the cleavage of the carbon-oxygen bond, facilitating the formation of a carbocation which can then react with Cl⁻ to form ethyl chloride (alkyl halide).
- **Conclusion**: This reaction can be used to prepare an alkyl halide.

2. **Reaction II: `CH₃CH₂OH + HCl →`**
- This is the same primary alcohol (ethanol) reacting with HCl but without the presence of ZnCl₂.
- While HCl can react with alcohols, the absence of ZnCl₂ means that the reaction is less efficient and may not lead to significant alkyl halide formation.
- **Conclusion**: This reaction is not reliable for preparing alkyl halides.

3. **Reaction III: `(CH₃)₃COH + HCl →`**
- This is a tertiary alcohol (tert-butanol) reacting with HCl.
- Tertiary alcohols can react directly with concentrated HCl to form alkyl halides without the need for ZnCl₂.
- **Conclusion**: This reaction can be used to prepare an alkyl halide.

4. **Reaction IV: `(CH₃)₂CHOH + HCl (anhy. ZnCl₂) →`**
- This is a secondary alcohol (isopropanol) reacting with HCl in the presence of anhydrous ZnCl₂.
- Similar to the primary alcohol, the presence of ZnCl₂ facilitates the reaction, allowing the formation of isopropyl chloride (alkyl halide).
- **Conclusion**: This reaction can also be used to prepare an alkyl halide.

### Final Conclusion:
The reactions that can be used for the preparation of alkyl halides are:
- Reaction I
- Reaction III
- Reaction IV

Thus, the correct answer is **Reaction I, Reaction III, and Reaction IV**.