Which is/are a purely surface phenomena :

Options

A. surface tension
B. adsorption
C. absorption
D. none of these

Answer

To determine which phenomena are purely surface phenomena, we need to analyze the options given and understand the definitions of surface tension, adsorption, and absorption.

### Step-by-Step Solution:

1. **Understanding Surface Phenomena**:
- Surface phenomena are processes that occur at the interface between two phases, such as solid-liquid, liquid-gas, or solid-gas. They do not involve the bulk of the material but are confined to the surface.

2. **Identifying Surface Tension**:
- Surface tension is the property of a liquid that allows it to resist an external force due to the cohesive nature of its molecules. It is a purely surface phenomenon because it occurs at the surface of the liquid and does not involve the liquid's interior.

3. **Identifying Adsorption**:
- Adsorption is the process by which atoms, ions, or molecules from a gas, liquid, or dissolved solid adhere to a surface. This process is also a purely surface phenomenon since it involves the accumulation of substances at the surface rather than within the bulk of the material.

4. **Identifying Absorption**:
- Absorption, on the other hand, is a process where a substance is taken up by another substance, resulting in a uniform distribution throughout the bulk. For example, when a sponge absorbs water, the water penetrates into the sponge, which is not a surface phenomenon.

5. **Conclusion**:
- Based on the definitions and characteristics of these processes, we conclude that surface tension and adsorption are purely surface phenomena, while absorption is not.

### Final Answer:
The purely surface phenomena are:
- Surface Tension
- Adsorption