Select the incorrect statment:

Options

A. The C. N. of cation occupying a tetrahedral hole is 4
B. The C.N of cation occupying a octahedral hole
is 6.
C. In Schottky defects,density of the lattice decreases.
D. In Frenkel defects, density of the lattice increases.

Answer

To solve the question of selecting the incorrect statement regarding coordination numbers and defects in solid-state chemistry, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze the first statement:**
- **Statement:** The coordination number of cation occupying tetrahedral hole is 4.
- **Explanation:** A tetrahedral hole is formed when four atoms are arranged in a tetrahedral geometry. In this arrangement, one cation is surrounded by four anions. Therefore, the coordination number is indeed 4.
- **Conclusion:** This statement is **correct**.

2. **Analyze the second statement:**
- **Statement:** The coordination number of cation occupying an octahedral hole is 6.
- **Explanation:** An octahedral hole is formed when six atoms are arranged in an octahedral geometry around a central cation. Thus, the coordination number for a cation in an octahedral hole is 6.
- **Conclusion:** This statement is **correct**.

3. **Analyze the third statement:**
- **Statement:** In Schottky defects, the density of the lattice decreases.
- **Explanation:** In Schottky defects, equal numbers of cations and anions are missing from the lattice. This results in a decrease in the overall mass of the lattice while the volume remains the same, leading to a decrease in density.
- **Conclusion:** This statement is **correct**.

4. **Analyze the fourth statement:**
- **Statement:** In Frenkel defect, the density of the lattice increases.
- **Explanation:** In a Frenkel defect, a cation leaves its original lattice position and occupies an interstitial site. Since there is no loss of ions from the lattice (only a displacement), the total number of ions remains the same, and thus the density does not increase; it remains unchanged.
- **Conclusion:** This statement is **incorrect**.

### Final Conclusion:
The incorrect statement is **option 4**: "In Frenkel defect, density of the lattice increases."

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