There is a small energy gap between the conduction and valence bands of

Options

A. copper
B. silver
C. sodium
D. aluminium

Answer

To solve the question regarding which material has a small energy gap between the conduction and valence bands, we will analyze the properties of the given materials: copper, silver, sodium, and aluminum.

### Step-by-Step Solution:

1. **Understanding Energy Bands**:
- In solids, electrons occupy energy levels that are grouped into bands. The two most important bands are the valence band (filled with electrons) and the conduction band (where electrons can move freely and conduct electricity).
- The energy gap between these two bands is crucial in determining the electrical properties of the material.

2. **Identifying the Materials**:
- The materials in question are copper, silver, sodium, and aluminum.
- Copper, silver, and aluminum are metals, while sodium is also a metal but has different properties due to its solid state.

3. **Analyzing Metals**:
- For metals like copper, silver, and aluminum, the conduction band and valence band overlap. This means there is no significant energy gap between them, allowing electrons to move freely and conduct electricity efficiently.
- Metals typically have high conductivity due to this overlap.

4. **Examining Sodium**:
- Sodium, while also a metal, has a different structure. It is a solid with a discrete energy level arrangement. This results in a small energy gap between the conduction band and the valence band.
- The presence of this energy gap means that sodium does not conduct electricity as efficiently as the other metals mentioned.

5. **Conclusion**:
- Based on the analysis, the material that has a small energy gap between the conduction and valence bands is **sodium**.

### Final Answer:
The correct option is **sodium**.

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