Assertion : At critical temperature, surface tension of liquids becomes zero.
Reason : At critical temperature, intermolecular forces for liquids and gases become equal. Liquids can expand without restriction.

Options

A. Statement-1, is true, Statement-2 is true, Statement-2 is correct explanation for statement-1
B. Statement-1 is true, statement-2 is true, statement-2 is NOT a correct explantion for statement-1
C. statement-1 is true, statement-2 is false
D. statement-1 is false statement-2 is true

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states that "At critical temperature, surface tension of liquids becomes zero."
- At the critical temperature, a substance reaches a point where it can no longer exist as a liquid or gas. This is the point where the properties of the liquid and gas phases become indistinguishable. As the temperature approaches the critical point, the kinetic energy of the molecules increases, and the intermolecular forces become weaker. Hence, the surface tension, which is a result of these intermolecular forces, approaches zero.

### Step 2: Understand the Reason
The reason states that "At critical temperature, intermolecular forces for liquids and gases become equal. Liquids can expand without restriction."
- At the critical temperature, the intermolecular forces in the liquid phase become equal to those in the gas phase. This means that the attractive forces that hold the liquid molecules together are balanced by the kinetic energy of the molecules. As a result, the liquid can expand freely, similar to a gas, leading to the conclusion that surface tension becomes negligible.

### Step 3: Evaluate the Relationship
Now, we need to determine if the reason correctly explains the assertion.
- Since the assertion is true (surface tension becomes zero at critical temperature) and the reason accurately describes why this happens (intermolecular forces become equal), we can conclude that the reason is indeed the correct explanation of the assertion.

### Conclusion
Both the assertion and the reason are true, and the reason correctly explains the assertion.

### Final Answer
Both the assertion and reason are true, and the reason is the correct explanation of the assertion.

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