Which material would be best to use as caps on iron bolts so the caps become the sacrificial anodes and the iron bolts the protected cathodes?

Which material would be best to use as caps on iron bolts so the caps become the sacrificial anodes and the iron bolts the protected cathodes?

• A. Brass
• B. Magnesium
• C. Tin
• D. Copper

Answer: (B)

When two metals are in electrical contact in an electrolyte, the more active metal becomes the anode and corrodes first, protecting the less active metal as the cathode. You want the cap to act as the sacrificial anode to save the iron bolt. Magnesium is the most electrochemically active among the options, so it will corrode preferentially and provide protective electrons to the iron, preventing the bolt from corroding. The other metals listed are more noble and won’t sacrifice themselves as readily, so they wouldn’t offer the same protection. Hence, magnesium is the best choice for the cap material.

When two metals are in electrical contact in an electrolyte, the more active metal becomes the anode and corrodes first, protecting the less active metal as the cathode. You want the cap to act as the sacrificial anode to save the iron bolt. Magnesium is the most electrochemically active among the options, so it will corrode preferentially and provide protective electrons to the iron, preventing the bolt from corroding. The other metals listed are more noble and won’t sacrifice themselves as readily, so they wouldn’t offer the same protection. Hence, magnesium is the best choice for the cap material.