A copper wire is used in a coil because of its:

Options

A. Small resistance
B. High conductivity
C. High resistance
D. Availability

Explanation

To determine why a copper wire is used in a coil, we can analyze the properties of copper and its electrical characteristics.

### Step-by-Step Solution:

1. **Understanding Resistance**: The resistance \( R \) of a wire is given by the formula:
\[ R = \frac{\rho L}{A} \]
where \( \rho \) is the resistivity of the material, \( L \) is the length of the wire, and \( A \) is the cross-sectional area.

2. **Properties of Copper**: Copper has a low resistivity compared to many other materials. This means that for a given length and cross-sectional area, a copper wire will have a lower resistance.

3. **Conductivity Relation**: Conductivity \( \sigma \) is the inverse of resistivity:
\[ \sigma = \frac{1}{\rho} \]
Since copper has a low resistivity, it has a high conductivity.

4. **Implications of High Conductivity**: High conductivity allows electricity to flow easily through the copper wire. This is crucial for applications such as coils, where efficient current flow is necessary.

5. **Availability and Practicality**: Copper is also widely available and relatively easy to work with, making it a practical choice for wiring and coils.

6. **Conclusion**: Therefore, the primary reason copper wire is used in a coil is due to its high conductivity, which allows for efficient electrical transmission.

### Final Answer:
Copper wire is used in a coil because of its **high conductivity**.