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 temperatures, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Bands in Solids**:
- In solids, the energy levels are organized into bands: the **valence band** (where electrons are present) and the **conduction band** (where electrons can move freely and contribute to conduction).
- The behavior of these bands varies among metals, semiconductors, and insulators.

2. **Characteristics of Metals**:
- In metals, the valence band and conduction band overlap. This means that there are free electrons available for conduction even at low temperatures.
- As a result, metals can conduct electricity very well without requiring additional energy to excite electrons from the valence band to the conduction band.

3. **Characteristics of Semiconductors**:
- Semiconductors have a small energy gap (typically around 1 eV) between the valence band and conduction band. At low temperatures, the electrons in the valence band need some thermal energy to jump to the conduction band, which is not available at very low temperatures.
- Therefore, semiconductors do not exhibit overlapping bands at low temperatures.

4. **Characteristics of Insulators**:
- Insulators have a larger energy gap between the valence band and conduction band. This gap is too large for electrons to jump from the valence band to the conduction band at low temperatures, making them poor conductors.

5. **Conclusion**:
- Since the valence band and conduction band overlap at low temperatures, the solid in question must be a **metal**. This is because metals have free electrons available for conduction, even at low temperatures.

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