Permanent hardness is due to presence of soluble salts of Mg and Ca in the form of chlorides and sulphates in `H_(2)O`. It can be removed by

Options

A. boiling
B. Clark's method
C. treatment with `Na_(2)CO_(3)`
D. all of these

Answer

To solve the question regarding the removal of permanent hardness in water, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Permanent Hardness**:
- Permanent hardness in water is primarily caused by the presence of soluble salts of calcium (Ca) and magnesium (Mg) in the form of chlorides (e.g., CaCl2, MgCl2) and sulfates (e.g., CaSO4, MgSO4).

2. **Identifying Removal Methods**:
- Unlike temporary hardness, which can be removed by boiling or using calcium hydroxide (Clark's method), permanent hardness requires different methods for removal.

3. **Using Sodium Carbonate (Na2CO3)**:
- One effective method to remove permanent hardness is by using sodium carbonate (Na2CO3). When sodium carbonate is added to water containing calcium and magnesium salts, it reacts with these salts to form insoluble carbonates.

4. **Chemical Reactions**:
- The reactions can be represented as follows:
- For calcium chloride:
\[ \text{CaCl}_2 + \text{Na}_2\text{CO}_3 \rightarrow \text{CaCO}_3 \downarrow + 2 \text{NaCl} \]
Here, calcium carbonate (CaCO3) precipitates out as a solid, while sodium chloride (NaCl) remains dissolved in water.

- For magnesium chloride:
\[ \text{MgCl}_2 + \text{Na}_2\text{CO}_3 \rightarrow \text{MgCO}_3 \downarrow + 2 \text{NaCl} \]
Similarly, magnesium carbonate (MgCO3) precipitates out.

5. **Separation of Precipitates**:
- The precipitated carbonates (CaCO3 and MgCO3) can then be removed from the water through simple filtration.

6. **Conclusion**:
- Therefore, the removal of permanent hardness can be effectively achieved by treating the water with sodium carbonate (Na2CO3).

### Final Answer:
Permanent hardness can be removed by treatment with Na2CO3 (sodium carbonate).

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