In a galvanic couple, which metal is most likely to corrode when two metals are in contact in an electrolyte?

• A. The more noble metal corrodes.
• B. Both corrode equally.
• C. The less active metal corrodes.
• D. The more active metal corrodes.

Answer: (D)

In a galvanic couple in an electrolyte, the metal that is more active (less noble) is the one that corrodes. Here’s why: when two dissimilar metals touch and are in a conductive solution, electrons flow from the more active metal to the less active one. The more active metal acts as the anode and oxidizes, releasing metal ions into the solution. The less active (noble) metal acts as the cathode and is protected from corrosion because reduction reactions occur there instead of oxidation. The electrolyte enables ion movement and completes the circuit, driving the corrosion of the active metal while the noble metal remains relatively uncorroded. For example, in a zinc-copper pair in saltwater, zinc corrodes and copper is spared, illustrating which metal tends to corrode.