NaCl becomes paramagnetic at high temperature due to

Options

A. Formation of F - centre
B. Molent state
C. Change in oxidation state
D. Conversion of `Na^(+)` to Na

Answer

To solve the question of why NaCl becomes paramagnetic at high temperatures, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding the Structure of NaCl**:
- Sodium chloride (NaCl) is an ionic compound consisting of Na⁺ and Cl⁻ ions arranged in a crystal lattice structure.

**Hint**: Recall that ionic compounds are made up of positively and negatively charged ions.

2. **Effect of High Temperature**:
- When NaCl is heated to high temperatures, it undergoes changes in its physical properties. The thermal energy can cause some of the ions to move more freely.

**Hint**: Consider how heat affects the movement and arrangement of particles in a solid.

3. **Heating in Sodium Vapor**:
- If NaCl is heated in the presence of sodium vapor, sodium atoms can deposit onto the surface of the NaCl crystal. This results in the formation of sodium ions (Na⁺) and chloride ions (Cl⁻) at the surface.

**Hint**: Think about what happens when sodium vapor interacts with the NaCl crystal.

4. **Formation of F-Centers**:
- The heating process leads to the loss of electrons from the sodium ions. These electrons can occupy vacancies created by the absence of Cl⁻ ions, known as F-centers (or color centers). An F-center is an anionic vacancy in the crystal lattice that is occupied by an unpaired electron.

**Hint**: Remember that F-centers are related to the presence of vacancies and unpaired electrons in the crystal structure.

5. **Increase in Unpaired Electrons**:
- The introduction of these unpaired electrons due to the formation of F-centers increases the number of unpaired electrons in the crystal. The presence of unpaired electrons is a key characteristic of paramagnetic substances.

**Hint**: Reflect on how unpaired electrons contribute to the magnetic properties of a material.

6. **Conclusion**:
- As a result of the formation of F-centers and the increase in unpaired electrons, NaCl exhibits paramagnetism at high temperatures.

**Hint**: Summarize the relationship between unpaired electrons and paramagnetism.

### Final Answer:
NaCl becomes paramagnetic at high temperatures due to the formation of F-centers, which are anionic vacancies occupied by unpaired electrons.