What are three requirements for a corrosion cell to form?

• A. A cathode
• B. An anode
• C. An electrolyte
• D. A cathode, an anode, and an electrolyte

Answer: (D)

A corrosion cell requires three elements to function: a site where oxidation occurs (the anode), a site where reduction occurs (the cathode), and a medium that allows ions to move (the electrolyte). The anode is where metal atoms lose electrons, creating metal ions. The cathode is where those electrons are consumed by a reduction reaction, often reducing oxygen or hydrogen ions. The electrolyte provides a path for ions to move and balance charges as the electrons flow through the external circuit from the anode to the cathode. If any one of these is missing, the electrochemical process cannot proceed: there would be no difference in potential without two different electrodes, or ions wouldn’t be able to move to balance charge without an electrolyte, or there would be no place for electrons to flow and for the redox reactions to occur. In practical terms, the corrosion process hinges on having all three present, so the combination that includes a cathode, an anode, and an electrolyte is the only one that supports a corrosion cell.