Pure O2 instead of air is used to oxidise the pig iron because : — d and f Block Elements Chemistry Question

💡 Solution & Explanation

Step 1: Passivity is a phenomenon where a metal loses its chemical reactivity due to the formation of a highly protective surface oxide film. Step 2: Concentrated nitric acid (conc. HNO3) is an extremely powerful oxidizing agent that oxidizes the surface of iron, forming a thin, impervious, and highly adherent layer of magnetic iron oxide (Fe3O4). Step 3: This oxide layer shields the underlying iron from further chemical attack. Hence, iron is made passive by treatment with conc. HNO3, matching option (c).