The amount of a liquid's cohesive force per unit of length is called

Options

A. depression
B. adhesion
C. apparent weight
D. surface tension

Explanation

To solve the question, we need to identify the term that describes the cohesive force of a liquid per unit length. Let's go through the steps:

### Step-by-Step Solution:

1. **Understanding Cohesive Forces**:
- Cohesive forces are the intermolecular forces that hold the molecules of a liquid together. They act between similar molecules.

2. **Identifying Related Terms**:
- There are two types of intermolecular forces: cohesive forces (between similar molecules) and adhesive forces (between different molecules).

3. **Analyzing the Options**:
- The question provides several terms: depression, adhesion, apparent weight, and surface tension. We need to determine which of these relates to cohesive forces.

4. **Defining Surface Tension**:
- Surface tension is defined as the force that acts at the surface of a liquid, caused by the cohesive forces between liquid molecules. It is a measure of how much force is exerted per unit length along the surface.

5. **Relating Surface Tension to Cohesive Forces**:
- Surface tension can be expressed mathematically as a force per unit length (T = F/L), where F is the cohesive force and L is the length over which this force acts.

6. **Conclusion**:
- Since surface tension represents the cohesive force per unit length in a liquid, the correct answer to the question is **surface tension**.

### Final Answer:
The amount of a liquid's cohesive force per unit of length is called **surface tension**.

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