Permanent hardness of water can be removed by adding

Options

A. `Na_2CO_3`
B. K
C. `Ca(OCl)Cl`
D. `Cl_2`

Answer

To solve the question regarding how to remove the permanent hardness of water, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Types of Hardness**:
- Water hardness is classified into two types: temporary hardness and permanent hardness.
- Temporary hardness is primarily due to the presence of bicarbonates and carbonates of calcium and magnesium.
- Permanent hardness is due to the presence of chlorides and sulfates of calcium and magnesium.

2. **Identify the Cause of Permanent Hardness**:
- Permanent hardness arises from dissolved salts, specifically chlorides and sulfates of calcium (Ca²⁺) and magnesium (Mg²⁺).

3. **Determine Methods to Remove Permanent Hardness**:
- To remove permanent hardness, we need to use a chemical that can react with the calcium and magnesium ions to form insoluble precipitates or to convert them into forms that do not contribute to hardness.

4. **Identify the Suitable Chemical**:
- One common method to remove permanent hardness is by adding washing soda, which is chemically known as sodium carbonate (Na₂CO₃).
- When washing soda is added to hard water, it reacts with calcium and magnesium ions to form insoluble carbonates, which precipitate out of the solution.

5. **Conclusion**:
- Therefore, the addition of washing soda (sodium carbonate) is an effective method to remove permanent hardness from water.

### Final Answer:
Permanent hardness of water can be removed by adding washing soda (sodium carbonate).

---