Which of the following is/are true statement(s)?

Options

A. `KO_2` is orange coloured because of F-centres
B. KCl is violet on heating with K-metal vapour because of F-centers
C. Crystals with defects are better conductor of electricity
D. CsCl also shows F-centre defect

Answer

To determine which of the statements are true, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Evaluate the first statement:**
- **Statement:** "KO2 is orange in color because of F centers."
- **Analysis:** KO2 (potassium superoxide) is actually yellow in color, not orange. The color is not due to F centers but rather due to the presence of superoxide ions.
- **Conclusion:** This statement is **false**.

2. **Evaluate the second statement:**
- **Statement:** "KCl is violet on heating with K metal vapor because of F centers."
- **Analysis:** When KCl is heated in the presence of potassium vapor, chloride ion vacancies (F centers) are created. These vacancies can trap electrons, which gives KCl a violet color. Therefore, the statement correctly describes the phenomenon.
- **Conclusion:** This statement is **true**.

3. **Evaluate the third statement:**
- **Statement:** "Crystals with defects are better conductors of electricity."
- **Analysis:** It is known that defects in crystals, such as stoichiometric defects, can enhance electrical conductivity by providing additional charge carriers. Thus, this statement is accurate.
- **Conclusion:** This statement is **true**.

4. **Evaluate the fourth statement:**
- **Statement:** "CsCl also shows F center defect."
- **Analysis:** CsCl (cesium chloride) primarily exhibits Schottky defects and does not typically show F center defects. F centers are more commonly associated with ionic compounds that can accommodate anions and electrons in the lattice.
- **Conclusion:** This statement is **false**.

### Final Assessment:
- **True Statements:** The second and third statements are true.
- **False Statements:** The first and fourth statements are false.

### Summary:
- True Statements: 2 and 3
- False Statements: 1 and 4