The phenomenon of adsorption arises due to unbalanced 

Options

A. valence force existing on the surface of solids
B. chemical forces of atoms in the molecules
C. coloumbic forces between electrons and nucleus
D. electrostatic repulsions between the nuclei

Answer

To solve the question regarding the phenomenon of adsorption and its underlying causes, we can break it down step by step:

### Step-by-Step Solution:

1. **Understanding Adsorption**:
- Adsorption is defined as the accumulation of molecules from a gas, liquid, or dissolved solid onto a surface. This process results in a film of the adsorbate (the substance being adsorbed) on the surface of the adsorbent (the solid or liquid surface).

2. **Surface Phenomenon**:
- It is important to note that adsorption is a surface phenomenon, meaning it primarily occurs at the interface between two phases (solid-liquid, solid-gas, etc.).

3. **Unbalanced Forces**:
- The key to understanding why adsorption occurs lies in the concept of unbalanced or residual forces. At the surface of a solid or liquid, the molecules experience different forces compared to those in the bulk. Molecules at the surface are not surrounded by other molecules on all sides, leading to unbalanced forces.

4. **Analyzing the Options**:
- Now, let's analyze the given options:
- **Option 1**: Balance force existing on the surface of solid - This is incorrect as adsorption occurs due to unbalanced forces.
- **Option 2**: Chemical process of atoms in the molecules - This is not the primary reason for adsorption.
- **Option 3**: Coulombic forces between electrons and nucleus - While these forces are fundamental in chemistry, they do not specifically explain adsorption.
- **Option 4**: Electrostatic repulsion between the nucleus - This does not directly relate to the phenomenon of adsorption.

5. **Conclusion**:
- The correct answer is that the phenomenon of adsorption arises due to unbalanced forces at the surface of the solid or liquid. Therefore, the correct option is **Option 1**: balance force existing on the surface of solids, as it highlights the importance of surface forces in adsorption.

### Final Answer:
The phenomenon of adsorption arises due to unbalanced forces at the surface of solids or liquids.

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