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 need to analyze the options provided and understand the types of hardness in water.

### Step-by-Step Solution:

1. **Identify Types of Hardness**:
- There are two types of hardness in water:
- **Temporary Hardness**: Caused by bicarbonates of calcium and magnesium (e.g., calcium bicarbonate, magnesium bicarbonate).
- **Permanent Hardness**: Caused by chlorides and sulfates of calcium and magnesium (e.g., calcium chloride, magnesium sulfate).

2. **Analyze the Options**:
- **Option 1: Treating with Washing Soda**:
- Washing soda (sodium carbonate) can be used to remove permanent hardness by precipitating calcium and magnesium ions as carbonates.
- **Option 2: Boiling**:
- Boiling can remove temporary hardness by converting bicarbonates into carbonates, which precipitate out.
- **Option 3: Adding Calgon**:
- Calgon (sodium hexametaphosphate) can also remove permanent hardness by forming soluble complexes with calcium and magnesium ions.
- **Option 4: Addition of Chlorine**:
- Chlorine is primarily used for disinfection and does not remove hardness from water.

3. **Conclusion**:
- Based on the analysis, the method that cannot remove hardness from water is the **addition of chlorine**. Therefore, the correct answer is **Option 4**.

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

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