Corrosion as electrochemical oxidation

Steps:

• Identify corrosion as an electrochemical process where metals oxidize by losing electrons.
• Check each option against the definition of oxidation in corrosion.
• Eliminate options contradicting known corrosion mechanisms or products.
• Confirm the option aligning with the anodic reaction in the corrosion cell.

Why D is correct:

• Corrosion involves anodic oxidation where metal atoms lose electrons to form positive ions, as in the half-reaction: Fe → Fe²⁺ + 2e⁻.

Why the others are wrong:

• A: Stainless steel resists corrosion via its chromium oxide passive layer, not requiring barriers.
• B: Iron corrosion initially forms iron(II) compounds, with hydrated iron(III) oxide as a secondary product from further oxidation.
• C: Sacrificial protection uses a more reactive metal (e.g., zinc) that corrodes preferentially, not a less reactive one.

Final answer: D