The angle of contact at the interface of water glass is `0^(@)` ethylalcohol-glass is `0^(@)` mercury glass is `140^(@)` and methyliodide-glass is `30^(@)` A glass capillary is put in a trough containing one of these four liquids. It is observed that the meniscus is convex. The liquid in the through is

Options

A. water
B. ethylalcohol
C. mercury
D. methyliodide

Explanation

To solve the problem, we need to analyze the information given about the angle of contact for different liquids when in contact with glass. We are particularly interested in the behavior of the meniscus formed when a liquid is placed in a glass capillary.

### Step-by-Step Solution:

1. **Understand the Concept of Angle of Contact**:
- The angle of contact (or wetting angle) is the angle formed between the tangent to the liquid surface and the solid surface (glass in this case) at the point of contact.
- If the angle is less than 90 degrees, the liquid wets the surface (concave meniscus). If the angle is greater than 90 degrees, the liquid does not wet the surface (convex meniscus).

2. **List the Given Angles of Contact**:
- Water-glass: 0 degrees (wetting, concave meniscus)
- Ethyl alcohol-glass: 0 degrees (wetting, concave meniscus)
- Mercury-glass: 140 degrees (non-wetting, convex meniscus)
- Methyl iodide-glass: 30 degrees (wetting, concave meniscus)

3. **Identify the Type of Meniscus Observed**:
- The problem states that the meniscus formed is convex. This indicates that the angle of contact must be greater than 90 degrees.

4. **Determine Which Liquid Corresponds to a Convex Meniscus**:
- From the list of angles of contact, only mercury has an angle of contact of 140 degrees, which is greater than 90 degrees. This means mercury will form a convex meniscus.

5. **Conclusion**:
- Since the only liquid that forms a convex meniscus in a glass capillary is mercury, we conclude that the liquid in the trough is mercury.

### Final Answer:
The liquid in the trough is **mercury**.

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