If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of container is

Options

A. acute angle
B. obtuse angle
C. `90^(@)`
D. `0^(@)`

Explanation

To solve the question, "If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of the container is," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Angle of Contact**:
- The angle of contact (or contact angle) is defined as the angle formed between the tangent to the liquid surface and the tangent to the solid surface (the wall of the container) at the point of contact.

2. **Visualizing the Situation**:
- Imagine a container (like a beaker) filled with a liquid (like water). The surface of the liquid is flat or horizontal due to the effects of surface tension.

3. **Identifying the Tangents**:
- At the surface of the liquid, we can draw a tangent line that is horizontal since the surface is flat.
- Now, consider the wall of the container (the beaker), which is vertical. We can also draw a tangent line to this vertical wall.

4. **Analyzing the Angles**:
- The tangent to the liquid surface (horizontal) and the tangent to the solid surface (vertical) will meet at a right angle.
- Since one tangent is horizontal and the other is vertical, the angle between them is 90 degrees.

5. **Conclusion**:
- Therefore, if the surface of the liquid is plane (horizontal), the angle of contact with the walls of the container is 90 degrees.

### Final Answer:
The angle of contact of the liquid with the walls of the container is **90 degrees**.

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