WAEC Chemistry 2011 Paper

Concept:A sacrificial anode must be a metal more reactive than iron.It corrodes first and protects the iron surface.Explanation:For protection, the metal must be placed above iron in the reactivity series.Magnesium ($\mathrm{Mg}$) is more reactive than iron ($\mathrm{Fe}$).So it acts as the anode and corrodes in place of iron.Copper, lead, and silver are less reactive than iron.Therefore, they cannot prevent iron from corroding.Answer:C. Magnesium