Among the following in which hydrates `H_(2)O` molecules only occupy the interstitial site

Options

A. `BaCl_(2)2H_(2)O`
B. `[[Ni(H_(2)O)_(6)]^(2+)](NO_(3)^(-))_(2)`
C. `CuSO_(4)5H_(2)O`
D. All of these

Answer

To solve the question, "Among the following in which hydrates H₂O molecules only occupy the interstitial site?", we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Interstitial Sites**:
- Interstitial sites in a crystal lattice are the spaces or voids between the atoms or ions in the crystal structure where smaller atoms or molecules can fit. In the context of hydrates, water molecules can occupy these sites.

2. **Analyzing Option 1: Barium Chloride Dihydrate (BaCl₂·2H₂O)**:
- In barium chloride dihydrate, the water molecules are present in the voids or interstitial sites of the crystal lattice. They do not form coordinate bonds with the barium or chloride ions. Thus, this option indicates that H₂O molecules only occupy interstitial sites.

3. **Analyzing Option 2: Nickel(II) Hexahydrate (Ni(H₂O)₆²⁺)**:
- In this case, the water molecules are coordinated to the nickel ion, forming coordinate bonds. This means that the water molecules are not merely occupying interstitial sites; they are integral to the structure of the complex. Therefore, this option does not satisfy the condition.

4. **Analyzing Option 3: Copper(II) Sulfate Pentahydrate (CuSO₄·5H₂O)**:
- In copper(II) sulfate pentahydrate, four water molecules coordinate with the copper ion, while one water molecule forms hydrogen bonds with the sulfate ion. Since some water molecules are involved in coordination and bonding, they do not occupy only interstitial sites. Thus, this option also does not satisfy the condition.

5. **Analyzing Option 4: (Not provided in the transcript)**:
- Since the transcript does not mention a fourth option, we can conclude that we have exhausted the analysis of the provided options.

6. **Conclusion**:
- The only option where H₂O molecules occupy only interstitial sites is **Option 1: Barium Chloride Dihydrate (BaCl₂·2H₂O)**.

### Final Answer:
The correct option is **Option 1: Barium Chloride Dihydrate (BaCl₂·2H₂O)**.