Alkyl benzene sulphonates can be used as detergents in hard water, unlike soaps, as

Options

A. They are highly soluble in water
B. Their `Ca^(++)//Mg^(++)` salts are water soluble
C. They are non-ionic
D. Their `Ca^(++)//Mg^(++)` salts are insoluble in water

Explanation

### Step-by-Step Solution:

1. **Understanding Hard Water**:
- Hard water contains high concentrations of minerals, primarily calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions can form insoluble salts with soap, which reduces its effectiveness as a cleaning agent.

2. **Soap and Its Limitations**:
- Soap is a sodium or potassium salt of fatty acids. When soap is added to hard water, the calcium and magnesium ions react with the soap to form insoluble precipitates (soap scum). This means that soap cannot effectively clean in hard water conditions.

3. **Alkyl Benzene Sulfonates**:
- Alkyl benzene sulfonates are synthetic detergents that have a sulfonate group (-SO₃Na) instead of a carboxylate group (-COO⁻) found in soaps. This structural difference allows them to function effectively in hard water.

4. **Why Alkyl Benzene Sulfonates Work in Hard Water**:
- Unlike soap, alkyl benzene sulfonates do not form insoluble precipitates with calcium and magnesium ions. Instead, they remain soluble in hard water, allowing them to effectively reduce surface tension and remove dirt and grease.

5. **Conclusion**:
- Therefore, alkyl benzene sulfonates can be used as detergents in hard water, while traditional soaps cannot, due to the formation of insoluble salts with the minerals present in hard water.