In the reaction where hypo acts as antichlor, hypo undergoes

Options

A. oxidation
B. reduction
C. disproportionation
D. halogenation

Answer

To solve the question regarding the reaction where hypo (sodium thiosulfate, Na2S2O3) acts as an antichlor, we will analyze the chemical reaction and determine what happens to hypo in that context.

### Step-by-Step Solution:

1. **Identify Hypo**:
- Hypo is sodium thiosulfate, which has the chemical formula Na2S2O3.

2. **Understand Antichlor**:
- An antichlor is a substance that removes excess chlorine from a solution. In this case, hypo is acting as an antichlor by reacting with chlorine (Cl2).

3. **Write the Reaction**:
- When sodium thiosulfate reacts with chlorine, the reaction can be represented as:
\[ \text{Na}_2\text{S}_2\text{O}_3 + \text{Cl}_2 \rightarrow \text{S} + \text{HCl} + \text{Na}_2\text{SO}_4 \]

4. **Determine Oxidation States**:
- In sodium thiosulfate (Na2S2O3), the oxidation state of sulfur is +2.
- In sodium sulfate (Na2SO4), the oxidation state of sulfur is +6.

5. **Analyze the Change in Oxidation State**:
- The oxidation state of sulfur increases from +2 in Na2S2O3 to +6 in Na2SO4. This indicates that oxidation is occurring.

6. **Conclusion**:
- Since the oxidation state of sulfur increases, we conclude that hypo (sodium thiosulfate) undergoes oxidation when it acts as an antichlor.

### Final Answer:
- Hypo undergoes **oxidation**.

---