Assertion : The angle of contact of a lilquid with a solid decreases with increase in temperature.
Reason : With increase in temperature, the surface tension of the liquid increases.

Options

A. both Assertion and Reason are true and the Reason in the correct explanation of the Assertion.
B. both Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
C. Assertion is true but the Reason is false.
D. both Assertion and Reason are false.

Explanation

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

### Step 1: Understand the Assertion
The assertion states that "The angle of contact of a liquid with a solid decreases with an increase in temperature."

- The angle of contact (or contact angle) is the angle formed between the tangent to the liquid surface and the solid surface at the point of contact.
- Generally, as temperature increases, the kinetic energy of the liquid molecules increases, which can lead to a decrease in the angle of contact, making the liquid spread more on the solid surface.

### Step 2: Evaluate the Assertion
However, the assertion claims that the angle of contact decreases with an increase in temperature, which is not universally true.

- In many cases, the angle of contact actually increases with temperature due to the decrease in surface tension. Therefore, the assertion is incorrect.

### Step 3: Understand the Reason
The reason states that "With an increase in temperature, the surface tension of the liquid increases."

- Surface tension is a property of liquids that tends to decrease with an increase in temperature. As temperature rises, the cohesive forces between liquid molecules weaken, leading to a decrease in surface tension.

### Step 4: Evaluate the Reason
Since the reason states that surface tension increases with temperature, this is also incorrect.

### Step 5: Conclusion
Both the assertion and the reason are false. Therefore, the correct conclusion is that both the assertion and the reason are incorrect.

### Final Answer
Both the assertion and the reason are false.