In electrochemical corrosion, what is the role of electrical contact between anodic and cathodic areas?

• A. It prevents corrosion
• B. It speeds only surface cleaning
• C. It is necessary for corrosion to proceed
• D. It changes color of metal

Answer: (C)

The electrical contact between anodic and cathodic areas provides a closed path for electrons, completing the electrical circuit that drives electrochemical corrosion. At the anodic site, metal atoms lose electrons (oxidation) and become ions. Those electrons must travel through the metal to the cathodic site, where a reduction reaction (often involving dissolved oxygen or hydrogen ions) occurs. Without this electron flow, charge would build up at the anodic spot and the oxidation reaction would quickly slow or stop, preventing ongoing corrosion. The electrolyte allows ions to move to balance charge, but the metal-to-metal electrical connection is what makes the redox reactions continuous. So the contact is necessary for corrosion to proceed.