Bleaching powder gives smell of chlorine because it

Options

A. is unstable
B. gives chlorine on exposure to atmosphere
C. is a mixture of chlorine and slaked lime
D. contains excess of chlorine .

Explanation

**Step-by-Step Solution:**

1. **Identify the Chemical Composition of Bleaching Powder:**
- The chemical formula for bleaching powder is \( \text{Ca(OCl)}_2 \) or calcium oxychloride.

2. **Understand the Reaction with Air:**
- When bleaching powder is exposed to air, it reacts with carbon dioxide (\( \text{CO}_2 \)) present in the atmosphere.

3. **Write the Reaction Equation:**
- The reaction can be represented as:
\[ \text{Ca(OCl)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{Cl}_2 \]
- Here, calcium carbonate (\( \text{CaCO}_3 \)) is formed along with chlorine gas (\( \text{Cl}_2 \)).

4. **Explain the Smell of Chlorine:**
- The chlorine gas produced during this reaction is what gives bleaching powder its characteristic smell of chlorine.

5. **Evaluate the Options:**
- The options provided in the question can be evaluated based on the above explanation:
- **Option 1:** Unstable - Incorrect, as bleaching powder is stable.
- **Option 2:** Gives chlorine on exposure to atmosphere - Correct, as it reacts with \( \text{CO}_2 \) to release chlorine gas.
- **Option 3:** Is a mixture of chlorine and slaked lime - Incorrect, as bleaching powder is not a mixture of these substances.
- **Option 4:** Smell of chlorine is produced by the reaction of carbon dioxide in the atmosphere with bleaching powder - Correct, as explained.

**Final Answer:**
Bleaching powder gives the smell of chlorine because it reacts with carbon dioxide in the atmosphere to produce chlorine gas.

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