Soft heavy metal melts at `30^(@)C` and is used in making heat sensitive thermometers the metal is

Options

A. Gallium
B. Sodium
C. Potassium
D. Caesium

Answer

To solve the question, we need to identify the metal that meets the criteria of being a soft heavy metal with a melting point of 30°C, which is also used in making heat-sensitive thermometers.

### Step-by-Step Solution:

1. **Identify the properties of the metal**:
- The metal should be soft.
- It should be heavy (high density).
- It should have a melting point around 30°C.
- It should be used in heat-sensitive thermometers.

2. **List potential metals**:
- We consider metals that are known for their low melting points. Common candidates include gallium, sodium, potassium, and cesium.

3. **Check the melting points**:
- Gallium: Melting point = 30°C
- Sodium: Melting point = 97°C
- Potassium: Melting point = 63°C
- Cesium: Melting point = 28°C

4. **Evaluate the options**:
- Among the listed metals, gallium is the only one that has a melting point exactly at 30°C.
- Cesium is close but does not meet the exact requirement as it melts at 28°C.

5. **Confirm the application**:
- Gallium is known to be used in heat-sensitive thermometers due to its unique melting point and properties.

6. **Conclusion**:
- Therefore, the metal that fits all the criteria is **gallium**.

### Final Answer:
The metal is **gallium**.

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