When limestone is heated `CO_(2)` gas is liberated. In metallurgy, this process is called as

Options

A. Calcination
B. Roasting
C. ore dressing
D. Sublimation

Explanation

To answer the question regarding the process that occurs when limestone is heated and liberates carbon dioxide gas in metallurgy, 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 a thermal decomposition reaction. The reaction can be represented as:
\[ \text{CaCO}_3 (s) \rightarrow \text{CaO} (s) + \text{CO}_2 (g) \]
Here, calcium oxide (CaO) is produced along with the release of carbon dioxide (CO₂) gas.

2. **Understand the Process**: This process of heating limestone to produce lime (calcium oxide) and carbon dioxide is known as **calcination**. Calcination is a thermal treatment process that is used to bring about a thermal decomposition.

3. **Differentiate from Other Processes**:
- **Roasting**: This is a different process where sulfide ores are converted into oxides in the presence of oxygen. For example, heating zinc sulfide (ZnS) in air produces zinc oxide (ZnO) and sulfur dioxide (SO₂).
- **Ore Dressing**: This refers to the concentration of ores by separating impurities from the valuable minerals.
- **Sublimation**: This is the process where a solid changes directly into vapor without becoming liquid, such as camphor.

4. **Conclusion**: Based on the above understanding, the process that occurs when limestone is heated to liberate carbon dioxide gas is called **calcination**.

### Final Answer:
The process is called **calcination**.

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