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Why does corrosion of iron require both water and oxygen?
AWater makes iron softer
BOxygen reacts with the H₂ released by iron
CWater + O₂ are needed to form Fe₂O₃ directly via combustion
DWater provides the electrolyte for the local cell; H⁺ (from dissolved CO₂/acidic oxides) and O₂ together oxidise iron via an electrochemical pathway
Answer & Solution
Correct answer: D. Water provides the electrolyte for the local cell; H⁺ (from dissolved CO₂/acidic oxides) and O₂ together oxidise iron via an electrochemical pathway
Corrosion is essentially an **electrochemical cell** on the metal surface: needs an **electrolyte (water with H⁺ from H₂CO₃)** to connect anodic and cathodic spots and oxygen to act as the cathodic oxidant. Dry air alone or pure de-oxygenated water alone won't corrode iron significantly.
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