Which of the following oxoacids of sulphur contains "S" in two different oxidation states ?

Options

A. `H_2S_2O_3`
B. `H_2S_2O_6`
C. `H_2S_2O_7`
D. `H_2S_2O_8`

Explanation

To determine which oxoacid of sulfur contains sulfur in two different oxidation states, we will analyze the oxidation states of sulfur in the given oxoacids one by one.

### Step 1: Analyze H₂S₂O₃
1. **Structure**: The structure of H₂S₂O₃ can be represented as HO-S(=O)-S(=O)-OH.
2. **Oxidation State Calculation**:
- For the first sulfur (S1), it is bonded to one hydroxyl group (OH) and one sulfur (S2) with a double bond (S=O).
- For the second sulfur (S2), it is bonded to two oxygens (double bonds) and one sulfur (S1).
- Using the bond breaking method:
- S1: +2 (due to two double bonds with oxygen) and S2: 0 (since it is bonded to another sulfur).
- Therefore, S1 is in the +2 oxidation state and S2 is in the 0 oxidation state.

### Step 2: Analyze H₂S₂O₆
1. **Structure**: The structure of H₂S₂O₆ can be represented as HO-S(=O)-O-S(=O)-OH.
2. **Oxidation State Calculation**:
- Both sulfur atoms are involved in symmetrical bonding with four oxygens.
- Both sulfur atoms are in the +6 oxidation state.
- Therefore, there are no different oxidation states here.

### Step 3: Analyze H₂S₂O₇
1. **Structure**: The structure of H₂S₂O₇ can be represented as HO-S(=O)-O-S(=O)-OH.
2. **Oxidation State Calculation**:
- Similar to H₂S₂O₆, both sulfur atoms are bonded to four oxygens.
- Both sulfur atoms have the same oxidation state of +6.
- Therefore, there are no different oxidation states here.

### Conclusion
From the analysis:
- H₂S₂O₃ has sulfur in two different oxidation states: +2 and 0.
- H₂S₂O₆ and H₂S₂O₇ have sulfur in the same oxidation state: +6.

Thus, the oxoacid of sulfur that contains "S" in two different oxidation states is **H₂S₂O₃**.