When lime stone is heated, `CO_(2)` is given off. The metallurgical operation is

Options

A. Smelting
B. Reduction
C. Calcination
D. Roasting

Answer

To solve the question about the metallurgical operation that occurs when limestone is heated and releases carbon dioxide (CO₂), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Chemical Reaction**:
When limestone, which is primarily composed of calcium carbonate (CaCO₃), is heated, it undergoes thermal decomposition. The reaction can be represented as:
\[ \text{CaCO}_3 (s) \rightarrow \text{CaO} (s) + \text{CO}_2 (g) \]
This shows that calcium carbonate decomposes into calcium oxide (CaO) and carbon dioxide (CO₂).

2. **Understand the Process**:
The process of heating limestone to produce calcium oxide and carbon dioxide is known as calcination. Calcination is a thermal treatment process in the absence or limited supply of air.

3. **Identify the Metallurgical Operation**:
In metallurgy, calcination is often used to extract metals from their ores. It is a crucial step in the production of lime (CaO) from limestone, which is then used in various metallurgical processes.

4. **Eliminate Incorrect Options**:
- **Melting**: This refers to the process of melting ores in furnaces, which is not applicable here.
- **Reduction**: This is the process of converting metal oxides to metals, which does not apply to the decomposition of limestone.
- **Roasting**: This involves heating ores in the presence of air to convert sulfides to oxides, which is also not applicable here.

5. **Conclusion**:
Since the question specifically refers to the operation that occurs when limestone is heated, the correct answer is **calcination**.

### Final Answer:
The metallurgical operation when limestone is heated and CO₂ is given off is **calcination**.