Which is correct statement?

Options

A. When temperature increases then number of defects decreases.
B. Schottky defect occurs when radius of cation is smalller
C. Frenkel defect occurs when radius of cation is smaller
D. none of these

Answer

To determine which statement is correct regarding defects in solids, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement:** When temperature increases, the number of defects decreases.

**Analysis:**
- As temperature increases, the energy of the particles in a crystal lattice also increases. This increased energy leads to greater disorder and more movement of particles, which can result in an increase in the number of defects, not a decrease. Therefore, this statement is **incorrect**.

### Step 2: Analyze the second statement
**Statement:** Schottky defect occurs when the radius of cation is small.

**Analysis:**
- A Schottky defect is characterized by the absence of equal numbers of cations and anions from their lattice sites, maintaining electrical neutrality. This defect typically occurs when the size difference between cations and anions is small or when their sizes are comparable. Thus, the statement that it occurs specifically when the radius of the cation is small is **incorrect**.

### Step 3: Analyze the third statement
**Statement:** Frenkel defect occurs when the radius of cation is smaller.

**Analysis:**
- A Frenkel defect is an interstitial defect where a cation (usually smaller in size) moves from its lattice position to an interstitial site. This movement is possible because the cation is small enough to fit into the interstitial space. Therefore, this statement is **correct**.

### Conclusion
After analyzing all the statements, the correct statement is:
- **Frenkel defect occurs when the radius of cation is smaller.**

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