Which of these statement is true for sodium thiosulphate ?

Options

A. it acts as an antichlor
B. it is used as an reducing agent in iodometric titration.
C. it reacts with hydrochloric acid to form `SO_(2)` and sulphur
D. it is used in photography as hypo to dissolves excess of AgBr as
soluble complex.

Explanation

To determine which statements are true for sodium thiosulfate (Na2S2O3), we can analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Identify the Chemical Formula**:
Sodium thiosulfate is represented by the formula Na2S2O3.

2. **Evaluate the First Statement**:
- **Statement**: It acts as an anti-chlore.
- **Analysis**: Sodium thiosulfate can react with chlorine to remove it from surfaces. The reaction can be represented as:
\[ \text{Na}_2\text{S}_2\text{O}_3 + 4\text{Cl}_2 + 5\text{H}_2\text{O} \rightarrow 2\text{NaHSO}_4 + 8\text{HCl} \]
- **Conclusion**: This statement is **true**.

3. **Evaluate the Second Statement**:
- **Statement**: It is used as a reducing agent in iodometric titration.
- **Analysis**: In iodometric titration, sodium thiosulfate reacts with iodine (I2) to form sodium tetrathionate (Na2S4O6) and sodium iodide (NaI):
\[ \text{Na}_2\text{S}_2\text{O}_3 + \text{I}_2 \rightarrow \text{Na}_2\text{S}_4\text{O}_6 + 2\text{NaI} \]
- **Conclusion**: This statement is **true**.

4. **Evaluate the Third Statement**:
- **Statement**: It reacts with hydrochloric acid to form SO2 and sulfur.
- **Analysis**: Sodium thiosulfate reacts with hydrochloric acid (HCl) to produce sulfur (S), sulfur dioxide (SO2), and water (H2O):
\[ \text{Na}_2\text{S}_2\text{O}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{S} + \text{SO}_2 + \text{H}_2\text{O} \]
- **Conclusion**: This statement is **true**.

5. **Evaluate the Fourth Statement**:
- **Statement**: It is used in photography as hypo to dissolve excess AgBr as a soluble complex.
- **Analysis**: Sodium thiosulfate is indeed used in photography (as hypo) to dissolve unreacted silver bromide (AgBr) by forming soluble complexes:
\[ 2\text{Na}_2\text{S}_2\text{O}_3 + \text{AgBr} \rightarrow \text{Na}_3\text{AgS}_2\text{O}_3 + \text{NaBr} \]
- **Conclusion**: This statement is **true**.

### Final Conclusion:
All four statements regarding sodium thiosulfate are **true**.