Which is an extensive property of the system?
Temperature
Volume
Refractive index
Viscosity.

Options

A. Temperature
B. Volume
C. Refractive index
D. Viscosity.

Explanation

To determine which of the given options is an extensive property of the system, we need to understand the definitions of extensive and intensive properties.

### Step-by-Step Solution:

1. **Define Extensive Properties**:
- Extensive properties are those that depend on the amount of matter or the size of the system. Examples include volume, mass, and energy.

2. **Define Intensive Properties**:
- Intensive properties are those that do not depend on the amount of matter or the size of the system. Examples include temperature, density, and refractive index.

3. **Analyze Each Option**:
- **Temperature**: This is an intensive property because it does not change with the amount of substance present in the system.
- **Volume**: This is an extensive property because it changes with the amount of substance present. For example, doubling the amount of substance will double the volume.
- **Refractive Index**: This is an intensive property as it remains constant regardless of the amount of substance.
- **Viscosity**: This is also an intensive property because it does not depend on the amount of substance present.

4. **Conclusion**:
- Among the options provided, the only extensive property is **Volume**.

### Final Answer:
The extensive property of the system is **Volume**.