Water shows convex meniscus in narrow ________ and _________ tubes.

Options

A. glass, plastic
B. glass, wax coated glass
C. wax coated glass, plastic
D. plastic, coloured glass

Explanation

To answer the question "Water shows convex meniscus in narrow ________ and _________ tubes," we need to identify the types of tubes where water exhibits a convex meniscus.

### Step-by-Step Solution:

1. **Understanding Meniscus**:
- A meniscus is the curve seen at the surface of a liquid in response to its container. It can be either convex (bulging upwards) or concave (curving downwards).

2. **Cohesive vs. Adhesive Forces**:
- Cohesive forces are the attractive forces between molecules of the same substance (like water molecules).
- Adhesive forces are the attractive forces between molecules of different substances (like water and the material of the tube).

3. **Identifying Tube Materials**:
- In narrow tubes, if the cohesive forces of water molecules are stronger than the adhesive forces between water and the tube's material, a convex meniscus will form.
- Conversely, if the adhesive forces are stronger, a concave meniscus will form.

4. **Types of Tubes**:
- **Wax Coated Glass Tubes**: The wax coating reduces the adhesive forces between the water and the glass, leading to a convex meniscus.
- **Plastic Tubes**: Plastic typically has lower adhesive forces with water compared to glass, resulting in a convex meniscus as well.

5. **Conclusion**:
- Therefore, the correct answer to fill in the blanks is: "Water shows convex meniscus in narrow **wax-coated glass** and **plastic** tubes."

### Final Answer:
Water shows convex meniscus in narrow **wax-coated glass** and **plastic** tubes.

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