Active corrosion on copper alloys is indicated by which of the following?

Correct Answer: Option C — A gray-green patina formation.

Copper alloys exposed to marine environments undergo oxidation, resulting in a characteristic gray-green patina. This layer is a stable copper carbonate or sulfate compound that forms on the surface, distinguishing it from active, destructive corrosion which typically presents as pitting or powdery deposits on other metallic substrates.