Which of the following statement is correct for the thiosulphate test ?

Options

A. Thiosulphate ions reduce `Fe^(3+)` to `Fe^(2+)` in aqueous solution
B. It can be prepared by oxidation of polysuphides
C. The reaction of thiosulphate with Hydrochloric acid generates Sulphur dioxide gas .
D. Chlorine oxidizes thiosulphate and this has led to the use of thiosulphate to remove excess chlorine in the bleaching industries

Explanation

To solve the question regarding the correctness of statements related to the thiosulphate test, we will analyze each statement one by one based on the information provided in the video transcript.

### Step-by-Step Solution:

1. **Understanding the Thiosulphate Test**:
- The thiosulphate test involves the use of thiosulphate ions (S2O3^2-) to reduce other ions, particularly Fe3+ ions, to Fe2+ ions.

2. **Statement Analysis**:
- **Statement A**: "Thiosulphate ions reduce Fe3+ to Fe2+ in aqueous solution."
- **Analysis**: This statement is correct. The reaction can be represented as:
\[ 2S_2O_3^{2-} + 2Fe^{3+} \rightarrow S_4O_6^{2-} + 2Fe^{2+} \]
- **Conclusion**: True.

- **Statement B**: "Thiosulphate can be prepared by oxidation of polysulphides."
- **Analysis**: This statement is also correct. For example, sodium polysulphide (Na2S3) can be oxidized to form sodium thiosulphate:
\[ 2Na_2S_3 + 3O_2 \rightarrow 2Na_2S_2O_3 + 2S \]
- **Conclusion**: True.

- **Statement C**: "Reaction of thiosulphate with hydrochloric acid generates sulfur dioxide gas."
- **Analysis**: This statement is correct. The reaction can be written as:
\[ Na_2S_2O_3 + 2HCl \rightarrow 2NaCl + H_2O + SO_2 + S \]
- **Conclusion**: True.

- **Statement D**: "Chlorine oxidizes thiosulphate, leading to its use in removing excess chlorine in bleaching industries."
- **Analysis**: This statement is also correct. The reaction can be represented as:
\[ Na_2S_2O_3 + 4Cl_2 + 5H_2O \rightarrow 2NaHSO_4 + 8HCl \]
- **Conclusion**: True.

3. **Final Conclusion**:
- Since all statements A, B, C, and D are correct, we conclude that the answer to the question is:
- All statements are correct.

### Final Answer:
All statements (A, B, C, D) regarding the thiosulphate test are correct.

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