By heating sodium in the atmosphere of chlorine, sodium chloride is obtained which is yellow in colour. The cause of yellow colour is:

Options

A. presence of face centered cubic lattice
B. presence of `Cl^-` ions in the crystal lattice
C. presence of `e^-` in the crystal lattice
D. presence of `Na^+` ions in the crystal lattice

Explanation

To solve the question regarding the yellow color of sodium chloride (NaCl) obtained by heating sodium in chlorine, we will follow these steps:

### Step 1: Understanding the Formation of Sodium Chloride
When sodium (Na) is heated in the presence of chlorine (Cl), a chemical reaction occurs where sodium loses an electron to form sodium ions (Na⁺) and chlorine gains an electron to form chloride ions (Cl⁻). The reaction can be represented as:
\[ 2 \text{Na} + \text{Cl}_2 \rightarrow 2 \text{NaCl} \]

### Step 2: Structure of Sodium Chloride
Sodium chloride crystallizes in a face-centered cubic (FCC) lattice structure. In this structure, Na⁺ ions and Cl⁻ ions alternate in the lattice.

### Step 3: Formation of F-Centers
During the formation of the NaCl crystals, if there are vacancies (missing ions) in the lattice, these vacancies can trap free electrons. These trapped electrons are known as F-centers (from the German word "Farbe," meaning color).

### Step 4: Absorption of Energy
The trapped electrons in the F-centers can absorb energy from visible light. When these electrons absorb energy, they can jump to a higher energy level. The specific energy levels they occupy correspond to the absorption of certain wavelengths of light.

### Step 5: Yellow Color Observation
The energy absorbed by these electrons corresponds to the wavelengths in the visible spectrum that are complementary to yellow. As a result, the absence of yellow light (due to its absorption) makes the sodium chloride appear yellow.

### Conclusion
Thus, the yellow color of sodium chloride is primarily due to the presence of electrons in the crystal lattice, specifically the F-centers that absorb visible light.

### Final Answer
The cause of the yellow color in sodium chloride is the presence of electrons in the crystal lattice (Option 3).

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