Which of the following given statesment is incorrect?

Options

A. F-centres generation is responsible factor for imparting colour to the crystal
B. Frenkel defect is usually shown by ionic compouns having low coordination number
C. Stoichiometry of crystal remains uneffected due to schottky defect
D. Density of crystal always increses due to susbtitutional impurity defect

Answer

To determine which of the given statements is incorrect, we will analyze each statement one by one.

### Step 1: Analyze Statement 1
**Statement 1:** "The F center generation is responsible for imparting color to the crystal."

**Analysis:**
- The F center refers to anionic vacancies in a crystal lattice that are occupied by electrons.
- For example, in sodium chloride (NaCl), when heated in the presence of sodium vapor, chloride ions (Cl-) leave their lattice positions, creating vacancies that are filled by electrons.
- These F centers absorb visible light, which imparts color to the crystal.

**Conclusion for Statement 1:** This statement is **correct**.

### Step 2: Analyze Statement 2
**Statement 2:** "The Frenkel defect is usually shown by ionic compounds having low coordination number."

**Analysis:**
- The Frenkel defect occurs when cations leave their lattice positions and occupy interstitial sites.
- This defect is typically found in ionic compounds with a significant size difference between cations and anions and low coordination numbers.
- Therefore, the statement accurately describes the conditions under which Frenkel defects occur.

**Conclusion for Statement 2:** This statement is **correct**.

### Step 3: Analyze Statement 3
**Statement 3:** "The stoichiometry of the crystal remains unaffected due to the Schottky defect."

**Analysis:**
- The Schottky defect involves the simultaneous absence of cations and anions from the lattice, maintaining the overall charge balance.
- Since equal numbers of cations and anions are missing, the stoichiometric ratio of the crystal remains unchanged.

**Conclusion for Statement 3:** This statement is **correct**.

### Step 4: Analyze Statement 4
**Statement 4:** "The density of crystal always increases due to the substitutional impurity defect."

**Analysis:**
- Substitutional impurity defects occur when an impurity atom replaces a host atom in the crystal lattice.
- The effect on density depends on the size and mass of the substituting impurity compared to the host atom.
- If the impurity atom is larger or lighter than the host atom, the density may decrease or remain the same, but it will not necessarily increase.

**Conclusion for Statement 4:** This statement is **incorrect**.

### Final Answer
The incorrect statement is **Statement 4**.

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