Select the incorrect statement ?

Options

A. Stoichiometry of crystal remain uneffected due to schottky defect
B. Frenkel defect is usually shown by ionic compounds having low coordination number
C. F-center generation is responsible for imparting color to the crystal
D. Density of crystal always increases due to substitutional impurity defect

Answer

To solve the question of selecting the incorrect statement, we will analyze each of the four statements provided. Here’s a step-by-step breakdown of the solution:

### Step 1: Analyze the First Statement
**Statement:** The stoichiometry of a crystal remains unaffected due to Schottky defect.

**Analysis:**
- Schottky defect occurs in ionic solids where equal numbers of cations and anions are missing from the lattice.
- This defect maintains the overall charge neutrality and stoichiometry of the crystal.

**Conclusion:** This statement is **correct**.

### Step 2: Analyze the Second Statement
**Statement:** Frankel defect is usually shown by ionic compounds having low coordination numbers.

**Analysis:**
- Frankel defect involves smaller cations leaving their original lattice sites to occupy interstitial sites.
- This type of defect is typically found in ionic compounds with low coordination numbers.

**Conclusion:** This statement is **correct**.

### Step 3: Analyze the Third Statement
**Statement:** F-Center generation is responsible for imparting color to the crystal.

**Analysis:**
- F-Centers (or Furbace Centers) are anionic vacancies in a crystal that are occupied by free electrons.
- The presence of these free electrons can absorb certain wavelengths of light, thus imparting color to the crystal.

**Conclusion:** This statement is **correct**.

### Step 4: Analyze the Fourth Statement
**Statement:** Density of a crystal always increases due to substitutional impurity defect.

**Analysis:**
- Substitutional impurity defects can lead to changes in density, but they do not always result in an increase.
- The density may remain constant or even decrease depending on the size and mass of the substituting atom compared to the original atom.

**Conclusion:** This statement is **incorrect**.

### Final Answer
The incorrect statement is **Option D**: "Density of a crystal always increases due to substitutional impurity defect."

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