Water is said to be permanently hard when it contains

Options

A. chlorides and sulphates of Mg and Ca
B. bicarbonates of Na and K
C. carbonates of Na and K
D. phosphates of Na and K.

Answer

**Step-by-Step Solution:**

1. **Understanding Water Hardness**: Water hardness is classified into two types: temporary hardness and permanent hardness. Temporary hardness is caused by the presence of bicarbonates, while permanent hardness is due to the presence of certain salts.

2. **Identifying Temporary Hardness**: Temporary hardness occurs when water contains bicarbonates of calcium (Ca) and magnesium (Mg). The chemical formula for calcium bicarbonate is Ca(HCO₃)₂.

3. **Identifying Permanent Hardness**: Permanent hardness is caused by the presence of soluble salts of calcium and magnesium, specifically their chlorides and sulfates. Common examples include:
- Calcium chloride (CaCl₂)
- Calcium sulfate (CaSO₄)
- Magnesium chloride (MgCl₂)
- Magnesium sulfate (MgSO₄)

4. **Analyzing the Options**: The question provides four options regarding what causes permanent hardness:
- A) Chlorides and sulfates of magnesium and calcium
- B) Bicarbonates of sodium and potassium
- C) Carbonates of sodium and potassium
- D) Phosphates of sodium and potassium

5. **Determining the Correct Answer**: Among the options, only option A (Chlorides and sulfates of magnesium and calcium) is correct because these compounds contribute to permanent hardness in water.

6. **Conclusion**: Therefore, water is said to be permanently hard when it contains chlorides and sulfates of magnesium and calcium.

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