Which of the following is NOT an example of adsorption ?

Options

A. Water on silica gel
B. Water on calcium chloride
C. hydrogen on finely divided nickel
D. Oxygen on metal surface

Answer

To determine which of the following is NOT an example of adsorption, we first need to understand the difference between adsorption and absorption.

### Step-by-Step Solution:

1. **Understanding Adsorption**:
- Adsorption is a surface phenomenon where molecules adhere to the surface of a solid or liquid. This process involves the accumulation of atoms, ions, or molecules from a gas, liquid, or dissolved solid on the surface of a solid or liquid.

2. **Understanding Absorption**:
- Absorption, on the other hand, is a bulk phenomenon where a substance is taken up by another substance, resulting in a uniform distribution throughout the bulk of the material.

3. **Analyzing the Options**:
- **Option 1: Water on Silica Gel**:
- This is an example of adsorption. Silica gel adsorbs water molecules on its surface.

- **Option 2: Water on Calcium Chloride**:
- This is an example of absorption. Calcium chloride (CaCl2) absorbs water into its structure, leading to a bulk change rather than just a surface interaction.

- **Option 3: Hydrogen on Finely Divided Nickel**:
- This is an example of adsorption. Hydrogen molecules adhere to the surface of the nickel particles.

- **Option 4: Oxygen on Metal Surface**:
- This is also an example of adsorption, as oxygen molecules adhere to the surface of the metal.

4. **Conclusion**:
- The only option that is NOT an example of adsorption is **Option 2: Water on Calcium Chloride**, as it represents absorption.

### Final Answer:
**The correct answer is Option 2: Water on Calcium Chloride.**