Which of the following is chemisorption 

Options

A. adsorption of `H_(2)` on Ni at high temperature
B. adsorption of `H_(2)` on charcoal
C. adsorption of moisture on silica gel
D. dehydration by using anhydrous `CaCl_(2)`

Answer

To determine which of the given options is an example of chemisorption, we need to understand the concept of chemisorption and how it differs from physisorption. Here’s a step-by-step solution:

### Step 1: Define Chemisorption
Chemisorption is a type of adsorption that involves a chemical reaction between the adsorbate (the substance being adsorbed) and the surface of the adsorbent (the material on which adsorption occurs). This process results in the formation of new chemical bonds.

**Hint:** Remember that chemisorption involves a chemical change and bond formation.

### Step 2: Analyze the Options
We need to examine each option provided to determine if it involves a chemical reaction and bond formation.

1. **Adsorption of H2 on nickel at high temperature**
- At high temperatures, hydrogen (H2) can react with nickel (Ni) to form nickel hydride (NiH). This indicates a chemical reaction and bond formation.

**Hint:** High temperature can facilitate chemical reactions, making this a strong candidate for chemisorption.

2. **Adsorption of H2 on charcoal**
- This process is typically a physical adsorption (physisorption) because it involves weak van der Waals forces and does not result in a chemical reaction.

**Hint:** Physisorption does not involve bond formation, so this is not chemisorption.

3. **Adsorption of moisture on silica gel**
- Similar to the previous case, this is also a physical adsorption. The water molecules adhere to the surface of silica gel through weak interactions, without forming new chemical bonds.

**Hint:** Look for chemical reactions; if there are none, it’s likely physisorption.

4. **Dehydration by using anhydrous CaCl2**
- This process involves the absorption of moisture by CaCl2, but it is a physical process rather than a chemical reaction. The water molecules are not chemically bonded to the CaCl2.

**Hint:** Absorption does not equal chemisorption unless new bonds are formed.

### Step 3: Conclusion
Based on the analysis, the only option that represents chemisorption is:

**Adsorption of H2 on nickel at high temperature.**

### Final Answer
The correct answer is: **Adsorption of H2 on nickel at high temperature.**