Which one of the following reagents is used for detection of unsaturation in alkenes

Options

A. `NaOH + CaO`
B. Cold dilute alkaline `KMnO_(4)`
C. `Cl_(2)//hv`
D. `KOH//C_(2)H_(5)OH`

Answer

To determine which reagent is used for the detection of unsaturation in alkenes, we can analyze the given options step by step.

### Step-by-Step Solution:

1. **Understanding Unsaturation**:
- Unsaturation in organic chemistry refers to the presence of double or triple bonds in a molecule, commonly found in alkenes and alkynes.

2. **Evaluating the Options**:
- **Option 1: Soda Lime**:
- Soda lime is primarily used for decarboxylation reactions and does not serve as a reagent for detecting unsaturation in alkenes. Therefore, this option is incorrect.

- **Option 2: Cold Dilute Alkaline KMnO4**:
- Cold dilute alkaline potassium permanganate (KMnO4) is known to react with alkenes. It acts as an oxidizing agent and can add across the double bond, leading to the decolorization of the purple solution of KMnO4. This indicates the presence of unsaturation. Thus, this is the correct answer.

- **Option 3: Cl2 (Chlorine)**:
- Chlorine is a halogen that can react with alkenes, but it is not specifically used for the detection of unsaturation. It can lead to addition reactions but does not provide a clear indication of unsaturation like KMnO4 does.

- **Option 4: KOH (Potassium Hydroxide)**:
- KOH is a strong base and is not used for detecting unsaturation in alkenes. It is more commonly used in reactions such as saponification or as a reagent in elimination reactions.

3. **Conclusion**:
- Based on the analysis, the reagent used for the detection of unsaturation in alkenes is **Cold Dilute Alkaline KMnO4**.

### Final Answer:
**Cold Dilute Alkaline KMnO4** is the reagent used for the detection of unsaturation in alkenes.

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