Available `Cl_2`​ is liberated from bleaching powder when it :-

Options

A. is heated
B. reacts with acid
C. reacts with `H_(2)O`
D. recs with `CO_(2)`

Answer

To determine when available \( Cl_2 \) (chlorine gas) is liberated from bleaching powder, we need to analyze the reactions of bleaching powder, which has the chemical formula \( Ca(OCl)_2 \) (calcium oxychloride or bleaching powder), with different substances.

### Step-by-Step Solution:

1. **Understanding Bleaching Powder**:
- Bleaching powder is primarily composed of calcium oxychloride, \( Ca(OCl)_2 \).
- It can release chlorine gas under certain conditions.

2. **Option A: Heating Bleaching Powder**:
- When bleaching powder is heated, it does not liberate chlorine gas.
- Therefore, this option is incorrect.

3. **Option B: Reacting with Acid**:
- When bleaching powder reacts with an acid, such as sulfuric acid (\( H_2SO_4 \)), it produces calcium sulfate (\( CaSO_4 \)), water (\( H_2O \)), and liberates chlorine gas (\( Cl_2 \)).
- The reaction can be represented as:
\[ Ca(OCl)_2 + H_2SO_4 \rightarrow CaSO_4 + H_2O + Cl_2 \]
- Thus, chlorine gas is liberated in this reaction, making this option correct.

4. **Option C: Reacting with Water**:
- When bleaching powder reacts with water, it forms calcium hydroxide (\( Ca(OH)_2 \)) and chlorine gas.
- The reaction can be represented as:
\[ Ca(OCl)_2 + 2H_2O \rightarrow Ca(OH)_2 + Cl_2 + 2HCl \]
- Therefore, chlorine gas is also liberated in this case, making this option correct.

5. **Option D: Reacting with Carbon Dioxide**:
- When bleaching powder reacts with carbon dioxide (\( CO_2 \)), it forms calcium carbonate (\( CaCO_3 \)) and liberates chlorine gas.
- The reaction can be represented as:
\[ Ca(OCl)_2 + CO_2 \rightarrow CaCO_3 + Cl_2 \]
- Hence, chlorine gas is liberated in this reaction as well, making this option correct.

### Conclusion:
From the analysis, chlorine gas is liberated when bleaching powder reacts with:
- B: Acid (e.g., sulfuric acid)
- C: Water
- D: Carbon Dioxide

Thus, the correct options are B, C, and D.