A hydrocarbon which decolourises `KMnO_(4)` but does not give any precipitate with ammoniated `AgNO_(3)`~

Options

A. Benzene
B. Acetylene
C. Butyne
D. `2-`Butene

Answer

To solve the question regarding a hydrocarbon that decolorizes KMnO4 but does not give any precipitate with ammoniated AgNO3, we can follow these steps:

### Step 1: Understand the Reagents
- **KMnO4** (Potassium permanganate) is a strong oxidizing agent that can oxidize alkenes and alkynes, leading to the decolorization of its purple color.
- **Ammoniated AgNO3** (Silver nitrate in ammonia) is used to test for terminal alkynes, which produce a white precipitate of silver alkanide.

### Step 2: Analyze the Hydrocarbon Types
- **Alkenes**: Unsaturated hydrocarbons with at least one double bond. They can decolorize KMnO4 but do not give a precipitate with ammoniated AgNO3.
- **Alkynes**: Unsaturated hydrocarbons with at least one triple bond. Terminal alkynes will react with ammoniated AgNO3 to form a precipitate.
- **Arenes (like benzene)**: Aromatic hydrocarbons that do not react with KMnO4.

### Step 3: Evaluate Each Hydrocarbon
1. **Alkynes**:
- Terminal alkynes will react with ammoniated AgNO3 and form a precipitate. Thus, they cannot be the answer.

2. **Arenes (Benzene)**:
- Benzene does not react with KMnO4 and therefore cannot decolorize it. Thus, it is not the answer.

3. **Alkenes (e.g., 2-butene)**:
- Alkenes like 2-butene can react with KMnO4, leading to the formation of diols and decolorization of KMnO4. They do not react with ammoniated AgNO3, hence no precipitate is formed.

### Step 4: Conclusion
Based on the analysis, the hydrocarbon that decolorizes KMnO4 but does not give any precipitate with ammoniated AgNO3 is **2-butene**.

### Final Answer
**2-butene** is the hydrocarbon that meets the criteria of the question.

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