Hardness of water cannot be removed by

Options

A. Treating with washing soda
B. Boiling
C. Adding calgon
D. Addition of chlorine.

Answer

To solve the question "Hardness of water cannot be removed by," we will analyze the different methods mentioned and their effectiveness in removing hardness from water.

### Step-by-Step Solution:

1. **Understand Hardness of Water**:
- Hardness in water is primarily due to the presence of certain minerals. There are two types of hardness:
- **Temporary Hardness**: Caused by bicarbonates of calcium and magnesium.
- **Permanent Hardness**: Caused by chlorides and sulfates of calcium and magnesium.

2. **Methods to Remove Hardness**:
- **Boiling**: This method is effective for removing temporary hardness. When water is boiled, bicarbonates decompose to form carbonate, which precipitates out as calcium carbonate.
- **Washing Soda**: This method is used to remove permanent hardness. Washing soda (sodium carbonate) reacts with calcium and magnesium ions to form insoluble precipitates.
- **Adding Calcium**: This method can also be used to remove permanent hardness by precipitating calcium as an insoluble compound.
- **Addition of Chlorine**: Chlorine is primarily used for disinfection and does not have any effect on the hardness of water.

3. **Evaluate Each Method**:
- **Treating with Washing Soda**: Effective for permanent hardness.
- **Boiling**: Effective for temporary hardness.
- **Adding Calcium**: Can help in removing permanent hardness.
- **Addition of Chlorine**: Does not remove hardness.

4. **Conclusion**:
- The method that does not remove hardness from water is the **addition of chlorine**.

### Final Answer:
Hardness of water cannot be removed by the addition of chlorine.

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