Galvanic corrosion occurs when dissimilar metals are electrically connected in an electrolyte; the more anodic metal corrodes while the more noble metal is protected.

• A. When two metals are cast together in solid state.
• B. When dissimilar metals are electrically connected in an electrolyte; the more anodic metal corrodes while the more noble metal is protected.
• C. When metal is heated to high temperature.
• D. When metal is pure and isolated.

Answer: (B)

Galvanic corrosion happens when different metals are in electrical contact and exposed to an electrolyte. The metal that is more anodic (less noble) loses electrons and corrodes, while the more noble metal accepts electrons and remains protected. The electrolyte allows ions to move, completing the circuit so the anodic metal corrodes preferentially. This exact situation—dissimilar metals connected in an electrolyte—drives galvanic corrosion, with the anodic metal corroding and the noble metal being protected. Other scenarios don’t describe galvanic corrosion: casting metals together in solid state lacks an electrolyte and a conductive path for ions; heating a metal speeds general oxidation but not the galvanic interaction between two metals; a pure, isolated metal has no partner to form a galvanic couple.