Permanent hardness can be removed by adding

Options

A. Slaked lime
B. Sodium bicarbonate
C. Washing soda
D. Calcium hydroxide

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 dissolved calcium and magnesium salts, such as calcium sulfate (CaSO₄) and magnesium chloride (MgCl₂). These salts do not precipitate out upon boiling, which is why the hardness is termed "permanent."

2. **Identifying the Options**:
- The options provided are:
1. Slate Land
2. Sodium Bicarbonate
3. Washing Soda (Sodium Carbonate, Na₂CO₃)
4. Calcium Hydroxide (Ca(OH)₂)

3. **Analyzing the Options**:
- **Slate Land**: This is not a chemical compound used for water treatment.
- **Sodium Bicarbonate (NaHCO₃)**: This can soften water temporarily but is not effective for permanent hardness.
- **Washing Soda (Sodium Carbonate, Na₂CO₃)**: This compound can react with calcium and magnesium ions in water to form insoluble carbonates, effectively removing hardness.
- **Calcium Hydroxide (Ca(OH)₂)**: While it can precipitate some hardness, it is not as effective as washing soda for permanent hardness.

4. **Chemical Reaction**:
- When washing soda (Na₂CO₃) is added to hard water, it reacts with calcium and magnesium ions:
\[ \text{Ca}^{2+} + \text{Na}_2\text{CO}_3 \rightarrow \text{CaCO}_3 \downarrow + 2\text{Na}^+ \]
\[ \text{Mg}^{2+} + \text{Na}_2\text{CO}_3 \rightarrow \text{MgCO}_3 \downarrow + 2\text{Na}^+ \]
- The calcium carbonate (CaCO₃) and magnesium carbonate (MgCO₃) precipitate out of the solution, thus softening the water.

5. **Conclusion**:
- Based on the analysis, the most effective option for removing permanent hardness is **Washing Soda (Sodium Carbonate, Na₂CO₃)**. Therefore, the correct answer is **Option 3**.

### Final Answer:
Permanent hardness can be removed by adding **Washing Soda (Sodium Carbonate, Na₂CO₃)**.

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