Assertion: Decolourisation of `KMnO_(4)` solution is used as a test for unsaturation.
Reason: Alkenes on reaction with cold, dilute aqueous solution of potasssium permanganate produce vicinal glycols.

Options

A. If both assertion and reson are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

To analyze the assertion and reason provided in the question, we will break down the concepts step by step:

### Step 1: Understanding the Assertion
The assertion states that the decolorization of KMnO₄ solution is used as a test for unsaturation. This means that when a compound with unsaturation (like alkenes) is present, it will cause the purple color of KMnO₄ to disappear.

**Hint:** Recall that KMnO₄ is a strong oxidizing agent and its color change indicates a chemical reaction.

### Step 2: Understanding the Reason
The reason given is that alkenes react with cold, dilute aqueous solutions of potassium permanganate to produce vicinal glycols. Vicinal glycols are compounds where two hydroxyl (–OH) groups are added to adjacent carbon atoms in the alkene.

**Hint:** Remember that alkenes have a double bond which can react with oxidizing agents to form alcohols.

### Step 3: The Reaction Mechanism
When alkenes react with cold, dilute KMnO₄, the double bond breaks, and the potassium permanganate adds hydroxyl groups across the double bond. This reaction can be summarized as follows:
1. The π bond of the alkene interacts with KMnO₄.
2. The reaction leads to the formation of vicinal glycols (1,2-diol).
3. During this reaction, KMnO₄ is reduced to MnO₂, which is colorless, resulting in the decolorization of the solution.

**Hint:** Focus on the fact that the presence of the double bond allows for the addition of hydroxyl groups, leading to the formation of a glycol.

### Step 4: Conclusion
Both the assertion and reason are correct:
- The decolorization of KMnO₄ does indicate the presence of unsaturation in a compound.
- The reaction of alkenes with KMnO₄ indeed produces vicinal glycols.

Thus, the assertion is true, and the reason correctly explains the assertion.

**Final Answer:** Both the assertion and reason are correct, and the reason correctly explains the assertion.