Which of the following can undergo a chemical reaction?

CuSO₄ $+$ Fe can undergo a chemical reaction.

In a reaction when a certain element displaces another due to its more reactivity, the reaction is known as a single displacement reaction. Iron metal can displace copper from its sulphate solution as iron is more reactive than copper. Iron displaces copper from copper sulphate solution to produce iron sulphate aqueous solution. Iron can be both in the state of solid as well as aqueous but copper sulphate must be in its aqueous state so that it can facilitate the reaction.