Reactivity series of metals

Metals don't all react equally readily. Magnesium burns with a dazzling white flame, iron rusts slowly in damp air, copper only darkens, and gold never changes. Listing metals from most to least reactive gives the reactivity series. A more reactive metal pushes a less reactive one out of a solution of its compound: an iron nail in blue copper sulfate solution gets coated with copper while the blue fades. The same idea protects ship hulls and pipes with a block of a more reactive metal that corrodes instead.