Valence forces cause 

Options

A. chemisorption
B. Ionic bond
C. sorption
D. adsorption involving multi layers

Answer

To solve the question "Valence forces cause:", we need to analyze the options provided and understand the concepts of adsorption and the types of forces involved.

### Step-by-Step Solution:

1. **Understanding Valence Forces**:
- Valence forces are the forces that hold atoms together in a molecule. They are responsible for the formation of chemical bonds, such as covalent bonds.

2. **Identifying Types of Adsorption**:
- There are two main types of adsorption:
- **Physical adsorption (physisorption)**: This involves weak van der Waals forces and can occur in multilayers.
- **Chemical adsorption (chemisorption)**: This involves the formation of strong chemical bonds (covalent or ionic) between the adsorbate and the adsorbent.

3. **Analyzing the Options**:
- **Option 1**: Chemisorption - This is correct as it involves valence forces leading to the formation of chemical bonds.
- **Option 2**: Ionic bonds - This is incorrect because ionic bonds are not primarily caused by valence forces in the context of adsorption.
- **Option 3**: Adsorption involving multilayer - This is incorrect for chemisorption, which typically forms a monolayer.
- **Option 4**: This option also refers to multilayer adsorption, which is not applicable for chemisorption.

4. **Conclusion**:
- The correct answer is **Option 1: Chemisorption**, as valence forces are responsible for the formation of strong bonds in this type of adsorption, leading to a unilayer formation.

### Final Answer:
**Valence forces cause chemisorption.**