Temporary hardness of water can be removed by simple boiling. Which one of the following causes of hardness is eliminated by boiling?

Introduction / Context:
Hardness in water arises mainly from dissolved calcium and magnesium salts. Temporary hardness (bicarbonates) can be removed by boiling, while permanent hardness (sulphates, chlorides, nitrates) requires chemical softening or ion exchange.

Given Data / Assumptions:

• Boiling is a physical treatment that decomposes bicarbonates.
• No chemical reagents are added.

Concept / Approach:
Boiling converts bicarbonates to carbonates, releasing carbon dioxide and precipitating calcium carbonate. Hence, calcium bicarbonate is removed by boiling (temporary hardness). Sulphates and nitrates of calcium and magnesium are not removed by mere boiling and represent permanent hardness.

Step-by-Step Solution:

Verification / Alternative check:
Textbook water chemistry confirms that only bicarbonate hardness is temporary and treatable by boiling.

Why Other Options Are Wrong:

• Calcium sulphate / Magnesium sulphate / Calcium nitrate: Permanent hardness, not removed by boiling.
• None of these: Incorrect because calcium bicarbonate is removable by boiling.

Common Pitfalls:

• Assuming all hardness can be boiled out; only temporary hardness is affected.

Final Answer:
Calcium bicarbonate