Why lime stone is added in the extraction of lead from galena ?

Options

A. It prevents the formation of `PbSO_4`
B. It remove the impurity of silica as fusible slag
C. It converts lead silicate to lead oxide
D. It remove the impurity of iron oxide as fusible slag

Explanation

### Step-by-Step Solution:

1. **Identify the Ore**: The primary ore of lead is galena, which is chemically represented as PbS (lead sulfide).

2. **Understanding the Role of Limestone**: Limestone is primarily composed of calcium carbonate (CaCO3). When limestone is heated during the extraction process, it undergoes thermal decomposition.

3. **Decomposition of Limestone**: The thermal decomposition of calcium carbonate (CaCO3) can be represented by the following reaction:
\[ \text{CaCO}_3 (s) \rightarrow \text{CaO} (s) + \text{CO}_2 (g) \]
This reaction produces calcium oxide (CaO) and carbon dioxide (CO2) gas.

4. **Formation of Slag**: The calcium oxide (CaO) produced from the decomposition of limestone reacts with silica (SiO2), which is an impurity present in the ore. The reaction can be represented as:
\[ \text{CaO} (s) + \text{SiO}_2 (s) \rightarrow \text{CaSiO}_3 (s) \]
The product of this reaction is calcium silicate (CaSiO3), which is also known as slag.

5. **Function of Slag**: The formation of slag is crucial because it helps to remove impurities from the lead extraction process. The slag is a fusible material that can be easily separated from the molten lead, thereby purifying the lead metal.

6. **Conclusion**: Therefore, limestone is added during the extraction of lead from galena to facilitate the removal of silica impurities by forming slag, which can be easily separated from the lead.