To determine in which reaction sulfur dioxide (SO₂) is acting as an oxidizing agent, we first need to understand what an oxidizing agent is. An oxidizing agent is a substance that gains electrons in a chemical reaction and, in doing so, causes another substance to be oxidized (lose electrons). ### Analyzing Each Option **Option A: SO₂ + 2HNO₃ → H₂SO₄ + NO₂ + Heat** - In this reaction, sulfur dioxide (SO₂) is being converted to sulfuric acid (H₂SO₄). - The nitrogen in nitric acid (HNO₃) is reduced to nitrogen dioxide (NO₂). - Here, SO₂ is being oxidized (losing electrons) to form H₂SO₄, while HNO₃ is reduced. - Therefore, SO₂ is not acting as an oxidizing agent; it is being oxidized itself. **Option B: 2SO₂ + 2H₂O + O₂ → 2H₂SO₄** - In this reaction, sulfur dioxide (SO₂) is reacting with water (H₂O) and oxygen (O₂) to form sulfuric acid (H₂SO₄). - The oxygen (O₂) is being reduced to form the sulfuric acid, while SO₂ is being oxidized to a higher oxidation state in H₂SO₄. - Again, SO₂ is not acting as an oxidizing agent; it is being oxidized. **Option C: SO₂ + 2H₂O + Cl₂ → H₂SO₄ + 2HCl** - In this reaction, sulfur dioxide (SO₂) reacts with water and chlorine gas (Cl₂) to produce sulfuric acid and hydrochloric acid (HCl). - Chlorine (Cl₂) is reduced to HCl, while SO₂ is oxidized to H₂SO₄. - Thus, SO₂ is not acting as an oxidizing agent; it is being oxidized. **Option D: SO₂ + 2H₂S → 3S + 2H₂O** - In this reaction, sulfur dioxide (SO₂) reacts with hydrogen sulfide (H₂S). - Here, H₂S is oxidized to elemental sulfur (S), while SO₂ is reduced (gaining electrons) to form elemental sulfur as well. - In this case, SO₂ is acting as an oxidizing agent because it is causing H₂S to lose electrons (be oxidized) while it itself is being reduced. ### Conclusion The correct answer is **D**. In this reaction, sulfur dioxide (SO₂) is acting as an oxidizing agent because it facilitates the oxidation of hydrogen sulfide (H₂S) to sulfur (S). ### Summary of Key Points - An oxidizing agent gains electrons and causes another substance to be oxidized. - In options A, B, and C, SO₂ is oxidized, not acting as an oxidizing agent. - In option D, SO₂ is reduced while oxidizing H₂S, making it the oxidizing agent. - Understanding oxidation states and electron transfer is crucial in identifying oxidizing and reducing agents in reactions.