Which of the following is NOT a common anodic inhibitor?

Zinc carbonate is not considered a common anodic inhibitor. Anodic inhibitors are substances that help to protect metals by forming a protective oxide layer on the anode, thereby preventing further corrosion. In this context, substances like nitrites, molybdates, and orthophosphates are widely used as anodic inhibitors in various applications, particularly in water treatment systems and cooling waters.

Nitrites, for instance, are effective in preventing corrosion in ferrous metals, while molybdates and orthophosphates can help to stabilize protective layers on metal surfaces. Zinc carbonate, on the other hand, primarily functions as a passivating agent and corrosion product in specific conditions rather than acting as a proactive anodic inhibitor. Its role is different from that of the recognized anodic inhibitors, which are specifically tailored to optimize corrosion resistance through anodic polarization. Therefore, identifying zinc carbonate as the option that does not belong among common anodic inhibitors aligns with its functional characteristics in corrosion control.