In the laboratory, sodium chloride is made by burning the sodium in the atmosphere of chlorine which is yellow in colour. The cause of yellow colour is:

Options

A. Presence of `Na^(+)` ions in the crystal lattice
B. Presence of `CI^(-)` ions in the crystal lattice
C. Presence of electron in the crystal lattice
D. Presence of face centered cubic crystal lattice

Answer

To determine the cause of the yellow color observed when sodium chloride (NaCl) is formed by burning sodium in chlorine, we need to analyze the options provided and understand the underlying chemistry.

### Step-by-Step Solution:

1. **Understanding the Formation of NaCl**:
Sodium chloride is formed when sodium (Na) reacts with chlorine (Cl2) gas. This reaction produces NaCl, which is an ionic compound.

2. **Observing the Color**:
The question states that the atmosphere of chlorine is yellow in color. We need to identify the reason for this yellow coloration.

3. **Identifying Possible Causes**:
The options provided are:
- A) Presence of any positive ion in the crystal lattice
- B) Presence of chlorine ion in the crystal lattice
- C) Presence of electron in the crystal lattice
- D) Presence of face-centered cubic crystal lattice

4. **Analyzing Each Option**:
- **Option A**: The presence of any positive ion in the crystal lattice does not specifically explain the yellow color.
- **Option B**: The presence of chlorine ions in the crystal lattice does not account for the yellow color either.
- **Option C**: The presence of electrons in the crystal lattice can lead to color phenomena. Specifically, these electrons can absorb energy from visible light and re-emit it, which can manifest as yellow light.
- **Option D**: The face-centered cubic crystal lattice structure is a characteristic of NaCl but does not explain the color.

5. **Conclusion**:
The yellow color is primarily due to the presence of electrons in the crystal lattice of NaCl. These electrons can absorb light energy and re-emit it in the form of yellow light. Therefore, the correct answer is **Option C**: Presence of electron in the crystal lattice.

### Final Answer:
The cause of the yellow color is the **presence of electrons in the crystal lattice** of sodium chloride.

---