The element which exists in liquid state for a wide range of temperature and can be used for measuring high temperature is

Options

A. `B`
B. `Al`
C. `Ga`
D. `In`

Explanation

To solve the question about which element exists in a liquid state for a wide range of temperatures and can be used for measuring high temperatures, we will analyze the given options: barium, aluminium, gallium, and indium.

### Step-by-Step Solution:

1. **Understand the Question**: We need to find an element that remains in the liquid state over a wide temperature range and is suitable for high-temperature measurement.

2. **Analyze the Options**:
- **Barium**: This is a solid metal at room temperature and has a high melting point (around 727 °C). It does not exist in a liquid state over a wide range of temperatures.
- **Aluminium**: Aluminium is also a solid at room temperature with a melting point of about 660 °C. It does not remain liquid over a wide range of temperatures.
- **Gallium**: Gallium has a melting point of about 29.76 °C, which means it can exist as a liquid at room temperature. It remains in a liquid state up to about 2204 °C (its boiling point). This gives it a wide range of temperatures in which it is liquid.
- **Indium**: Indium has a melting point of about 156.6 °C and a boiling point of 2072 °C. While it is liquid over a range of temperatures, it does not have as wide a range as gallium.

3. **Conclusion**: Among the options, gallium is the only element that exists in a liquid state from approximately 30 °C to 2204 °C. This wide range makes it suitable for high-temperature thermometry.

4. **Final Answer**: The element which exists in liquid state for a wide range of temperature and can be used for measuring high temperature is **gallium**.