Which metal is most likely to corrode?

Magnesium is the most likely to corrode among the metals listed. This susceptibility to corrosion can be attributed to its high reactivity and position in the electrochemical series, where it is one of the more active metals. When exposed to water or moisture, magnesium readily reacts and forms magnesium hydroxide, which can contribute to corrosion.

In comparison, while iron is also known for corrosion, particularly as rust (iron oxide) in the presence of oxygen and moisture, it often forms protective oxides that can slow down the process under certain conditions. Lead has a relatively low corrosion rate due to the formation of a protective oxide layer, making it more resistant. Aluminum can develop an oxide layer that protects it from further corrosion, which can significantly enhance its durability in various environments, particularly when compared to magnesium. Thus, magnesium's intrinsic properties make it the metal most prone to aggressive corrosion in typical environmental conditions.