Assertion : Acetylene forms acetylide but ethylene does not.
Reason : Acetylene is lighter than air.

Options

A. If both assertion and reason 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 given assertion and reason, we will break down the statements and evaluate their validity step by step.

### Step 1: Understanding the Assertion
**Assertion:** Acetylene forms acetylide but ethylene does not.

- **Explanation:** Acetylene (C₂H₂) is a terminal alkyne, which means it has a hydrogen atom attached to one of its carbon atoms that can be removed. When acetylene reacts with a strong base (like sodium amide), it can form an acetylide ion (C₂⁻), which is a negatively charged species. Ethylene (C₂H₄), on the other hand, is an alkene and does not have a terminal hydrogen that can be removed in the same way. Therefore, it cannot form an acetylide ion.

### Step 2: Understanding the Reason
**Reason:** Acetylene is lighter than air.

- **Explanation:** Acetylene is indeed lighter than air due to its lower molecular weight compared to the average molecular weight of air. This statement is true, but it does not explain why acetylene can form acetylide ions while ethylene cannot.

### Step 3: Evaluating the Relationship
- The assertion is true because acetylene can form acetylide ions while ethylene cannot.
- The reason is also true, but it does not provide a correct explanation for the assertion. The ability of acetylene to form acetylide ions is related to its structure and acidity, not its density compared to air.

### Conclusion
- **Final Evaluation:** Both the assertion and the reason are true, but the reason is not the correct explanation for the assertion.

### Answer:
- The assertion is true, and the reason is true, but the reason does not explain the assertion.

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