A water sample is said to contain permanent hardness if water contains

Options

A. sulphates and chlorides of calcium and magnesium
B. carbonates of calcium and magnesium
C. bicarbonates of calcium and magnesium
D. sulphates and chlorides of sodium and potassium.

Explanation

To determine what causes permanent hardness in a water sample, we can follow these steps:

### Step 1: Understand the Concept of Hardness in Water
Hardness in water refers to the presence of certain minerals that can affect its quality. It is primarily categorized into two types: temporary hardness and permanent hardness.

**Hint:** Remember that hardness is related to the presence of certain ions in water.

### Step 2: Identify the Causes of Temporary Hardness
Temporary hardness is mainly caused by the presence of bicarbonates of calcium (Ca(HCO₃)₂) and magnesium (Mg(HCO₃)₂). This type of hardness can be removed by boiling the water, which precipitates these bicarbonates.

**Hint:** Temporary hardness can be treated by boiling water.

### Step 3: Identify the Causes of Permanent Hardness
Permanent hardness, on the other hand, is due to the presence of soluble salts that do not precipitate upon boiling. The primary contributors to permanent hardness are the sulphates and chlorides of calcium and magnesium.

**Hint:** Permanent hardness cannot be removed by boiling.

### Step 4: Conclusion
Based on the understanding of the types of hardness in water, we conclude that a water sample is said to contain permanent hardness if it contains sulphates and chlorides of calcium and magnesium.

**Final Answer:** A water sample is said to contain permanent hardness if it contains sulphates and chlorides of calcium and magnesium.

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