The valence band and conduction band of a solid overlap at low temperature, the solid may be

Options

A. a metal
B. a semiconductor
C. an insulator
D. none of these

Answer

To solve the question regarding the overlap of the valence band and conduction band of a solid at low temperature, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Bands**:
- The valence band is the highest energy band that is fully occupied by electrons at absolute zero temperature.
- The conduction band is the band above the valence band that is typically empty at absolute zero but can be occupied by electrons when energy is provided.

2. **Identify the Overlap Condition**:
- The question states that the valence band and conduction band overlap at low temperatures. This condition is crucial for determining the type of solid.

3. **Analyze the Types of Solids**:
- **Metals**: In metals, the valence band and conduction band overlap. This means that there are available energy states for electrons to move freely, allowing for electrical conductivity.
- **Semiconductors**: In semiconductors, the conduction band and valence band are separated by a small energy gap. At low temperatures, the bands do not overlap, but some electrons can be thermally excited to the conduction band.
- **Insulators**: In insulators, there is a large energy gap between the valence band and conduction band, preventing overlap and making it difficult for electrons to move to the conduction band.

4. **Conclusion**:
- Since the question specifies that the valence band and conduction band overlap at low temperatures, the only type of solid where this occurs is a **metal**. Therefore, the correct answer is that the solid may be a **metal**.

### Final Answer:
The solid may be a **metal**.

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