Answer : 3. "nitrous acid"
Explanation :

Answer: C) nitrous acid Explanation: Nitrous acid act as an oxidising agent because it oxidises potassium iodide to iodine. It is also a reducing agent because it decolourises acidified potassium permanganate solution. Nitric acid acts only as an oxidising agent Ammonia acts only as a reducing agent Nitrogen peroxide acts only as an oxidising agent.