Which elements exhibit passivity when exposed to conc. HNO3?
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Answer: D. All of the above
Explanation
Iron, aluminum, and chromium become passive when treated with concentrated nitric acid due to oxide formation. The acid forms a thin, tightly adherent protective metal oxide film that prevents further acid attack. This passivation layer halts the dissolution of the underlying metal, protecting it from ongoing chemical corrosion. Passivity refers to a phenomenon where active metals become corrosion-resistant due to surface oxide film formation. Concentrated nitric acid is a powerful oxidizing agent that rapidly creates these protective microscopic barriers. Transition metals like iron and chromium readily form stable passivating oxide coatings under oxidizing conditions.
Option A lists only iron, ignoring the fact that aluminium and chromium exhibit identical passivity behavior. Option B contains an incomplete symbol intended for aluminium, which fails to account for the other reactive metals. Option C names only chromium, failing to include iron and aluminium which also passivate in concentrated acid.
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