Alcoholic solution of caustic potash is a specific reagent for

Options

A. Dehydration
B. Dehydrohalogenation
C. Dehydrogenation
D. Hydration.

Answer

To solve the question regarding the specific reagent for alcoholic solution of caustic potash, we will follow these steps:

### Step-by-Step Solution:

1. **Identify Caustic Potash**:
- Caustic potash is the common name for potassium hydroxide (KOH).

2. **Understand the Nature of the Solution**:
- The question specifies an alcoholic solution of KOH. This means KOH is dissolved in alcohol (usually ethanol).

3. **Determine the Reaction Type**:
- An alcoholic solution of KOH is known to facilitate a specific type of reaction called dehydrohalogenation. This involves the elimination of hydrogen and a halogen atom from a haloalkane.

4. **Example Reaction**:
- Consider the reaction of bromoethane (CH3CH2Br) with alcoholic KOH:
\[ \text{CH}_3\text{CH}_2\text{Br} + \text{KOH (alcoholic)} \rightarrow \text{CH}_2=\text{CH}_2 + \text{HBr} \]
- Here, bromoethane loses a hydrogen atom and a bromine atom to form ethene (an alkene) and hydrogen bromide (HBr).

5. **Contrast with Aqueous KOH**:
- If bromoethane were treated with aqueous KOH, the reaction would yield ethanol (an alcohol) instead of an alkene. This highlights the specificity of the alcoholic solution of KOH for dehydrohalogenation.

6. **Evaluate the Options**:
- The options provided are:
1. Dehydration
2. Dehydrohalogenation
3. Dehydrogenation
4. Hydration
- Based on the above analysis, the correct answer is **dehydrohalogenation**.

### Final Answer:
The alcoholic solution of caustic potash is a specific reagent for **dehydrohalogenation**.

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