Answer
What happens is that the iron will displace the Cu²⁺ from the copper sulfate solution. The following is the chemical equation for the reaction.
Fe + CuSO₄ → FeSO₄ + Cu
(i) This reactivity series helps us understand this displacement reaction taking place. The reactivity series is a series of metals, in order of reactivity from highest to lowest. It is used to determine the products of single displacement reactions, whereby a metal e.g Fe will replace another metal e.g Cu in a solution if the former is higher in the series than the latter.
Hence, the surface of the iron nail will have a brown coating of copper formed on it, and the color of the copper sulfate solution which was initially blue changes to light green.
The reactivity series is otherwise called the activity series. The figure is the reactivity series of metals.