Hardness of water may be tempoarary or permanent .Permanent hardness is due to the presence of

Options

A. Chlorides of Ca and Mg in water
B. sulphates of Ca and Mg in water
C. hydrogen carbonates of Ca and Mg in water
D. carbonates of alkalie metals in water

Explanation

**Step-by-Step Solution:**

1. **Understanding Hardness of Water**: Water hardness is classified into two types: temporary and permanent hardness. Temporary hardness is primarily caused by the presence of bicarbonates, while permanent hardness is caused by other salts.

2. **Identifying Permanent Hardness**: Permanent hardness is due to the presence of specific salts in water. The main contributors to permanent hardness are the chlorides and sulfates of calcium and magnesium.

3. **Analyzing the Components**:
- **Chlorides of Calcium and Magnesium**: These salts contribute to permanent hardness. When dissolved in water, they do not precipitate out upon boiling.
- **Sulfates of Calcium and Magnesium**: Similar to chlorides, sulfates also contribute to permanent hardness and remain dissolved in water even after boiling.

4. **Excluding Other Options**:
- **Hydrogen Carbonates of Calcium and Magnesium**: These are responsible for temporary hardness, as they can be removed by boiling.
- **Carbonates of Alkali Metals**: These do not contribute to either type of hardness in significant amounts.
- **Bicarbonates**: These are associated with temporary hardness and can be removed by boiling.

5. **Conclusion**: Therefore, the correct answer to the question regarding the cause of permanent hardness in water is the presence of chlorides and sulfates of calcium and magnesium.

**Final Answer**: Permanent hardness is due to the presence of chlorides and sulfates of calcium and magnesium.

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