The angle of contact of mercury glass surface is

Options

A. `0^@`
B. `80^@`
C. `120^@`
D. `135^@`

Answer

To determine the angle of contact of mercury on a glass surface, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept of Angle of Contact**:
The angle of contact (or contact angle) is the angle formed between the tangent to the liquid surface at the point of contact and the solid surface. It indicates how a liquid interacts with a solid surface.

2. **Identifying the Liquids and Solids**:
In this case, we are dealing with mercury (a liquid) and glass (a solid). Mercury is known for its high surface tension and its behavior on glass surfaces.

3. **Behavior of Mercury on Glass**:
When mercury is placed on a glass surface, it tends to form a convex shape due to its cohesive forces being stronger than the adhesive forces between mercury and glass.

4. **Drawing the Situation**:
Imagine a drop of mercury resting on a glass surface. At the point where the mercury drop meets the glass, we can visualize a tangent line drawn to the surface of the mercury drop.

5. **Measuring the Angle of Contact**:
The angle formed between the tangent to the mercury drop and the glass surface at the point of contact is the angle of contact. For mercury on glass, this angle is typically around 135 degrees.

6. **Conclusion**:
Therefore, the angle of contact of mercury on a glass surface is approximately 135 degrees.

### Final Answer:
The angle of contact of mercury on a glass surface is approximately **135 degrees**.

---