When air is blown from mouth into a test - tube containing lime water, the lime water turned milky due to the presence of

Options

A. oxygen
B. carbon dioxide
C. nitrogen
D. water vapour

Explanation

**Step-by-Step Solution:**

1. **Understanding Lime Water**: Lime water is a solution of calcium hydroxide (Ca(OH)₂) in water. It is commonly used in experiments to test for carbon dioxide.

2. **Blowing Air into Lime Water**: When air is blown from the mouth into a test tube containing lime water, the air contains various gases, including carbon dioxide (CO₂).

3. **Reaction of Carbon Dioxide with Lime Water**: The carbon dioxide present in the exhaled air reacts with the calcium hydroxide in the lime water. The chemical reaction can be represented as:
\[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \]
Here, calcium carbonate (CaCO₃) is formed along with water.

4. **Formation of Calcium Carbonate**: Calcium carbonate is insoluble in water, and it precipitates out of the solution, causing the lime water to turn milky.

5. **Conclusion**: Therefore, the lime water turns milky due to the presence of carbon dioxide in the air blown from the mouth, which reacts with the calcium hydroxide to form calcium carbonate.

6. **Final Answer**: The correct answer is carbon dioxide (CO₂).

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