`H_(2)S` acts only as reducing agent while `SO_(2)` can act both as a reducing agent and as an oxidising agent. How will you account for it ?

Options

A. S in`H_(2)` has –2 oxidation state
B. S in`SO_(2)` has oxidation state +4
C. Hydrogen in `H_(2)S`is more positive than oxygen
D. Oxygen is more negative in `SO_(2)`

Explanation

To understand why hydrogen sulfide (H₂S) acts only as a reducing agent while sulfur dioxide (SO₂) can act both as a reducing agent and as an oxidizing agent, we need to analyze the oxidation states of sulfur in both compounds and the definitions of reducing and oxidizing agents.

### Step-by-Step Solution:

1. **Define Oxidizing and Reducing Agents**:
- An **oxidizing agent** is a substance that gains electrons in a chemical reaction and is reduced.
- A **reducing agent** is a substance that loses electrons in a chemical reaction and is oxidized.

2. **Determine the Oxidation State of Sulfur in H₂S**:
- In H₂S, the oxidation state of sulfur (S) can be calculated as follows:
\[ \text{Let the oxidation state of S be } x. \]
The equation for the compound is:
\[ x + 2(+1) = 0 \quad \text{(since there are 2 hydrogen atoms)} \]
Simplifying this gives:
\[ x + 2 = 0 \implies x = -2. \]
- Therefore, the oxidation state of sulfur in H₂S is -2.

3. **Determine the Oxidation State of Sulfur in SO₂**:
- In SO₂, the oxidation state of sulfur can be calculated similarly:
\[ \text{Let the oxidation state of S be } x. \]
The equation for the compound is:
\[ x + 2(-2) = 0 \quad \text{(since there are 2 oxygen atoms)} \]
Simplifying this gives:
\[ x - 4 = 0 \implies x = +4. \]
- Therefore, the oxidation state of sulfur in SO₂ is +4.

4. **Analyze the Range of Oxidation States for Sulfur**:
- The oxidation states of sulfur can range from -2 (in H₂S) to +6 (in compounds like H₂SO₄).
- In H₂S, sulfur is already at its lowest oxidation state (-2), which means it can only act as a reducing agent by donating electrons.
- In SO₂, sulfur is at a +4 oxidation state, allowing it to either gain electrons (to become -2, acting as a reducing agent) or lose electrons (to become +6, acting as an oxidizing agent).

5. **Conclusion**:
- H₂S can only reduce other substances because sulfur cannot go lower than -2.
- SO₂ can both reduce (by going from +4 to -2) and oxidize (by going from +4 to +6) due to its ability to change its oxidation state.