Give a chemical test to distinguise between but `-1-`ene and but `-2-`ene.

Explanation

To distinguish between but-1-ene and but-2-ene, we can use a chemical test involving acidic potassium permanganate (KMnO4). Here's a step-by-step solution:

### Step 1: Understand the Structures
- **But-1-ene** has the structure: CH2=CH-CH2-CH3
- **But-2-ene** has the structure: CH3-CH=CH-CH3

### Step 2: Perform the Reaction with Acidic KMnO4
- When but-1-ene is treated with acidic KMnO4, it undergoes oxidation. The double bond reacts with KMnO4, leading to the formation of butanoic acid (H-COOH) which is unstable and decomposes to produce carbon dioxide (CO2) gas.
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