In the given electrochemical reaction:2Fe aq + Mg s 2Fe aq + Mg aq Each Fe ion is reduced to Fe, which means it gains one electron. Since there are two Fe ions, a total of 2 electrons are gained in the reduction half-reaction.Mg s is oxidized to Mg aq , which means it loses two electrons.So, the total number of electrons transferred in this reaction is 2 from the reduction of Fe ions + 2 from the oxidation of Mg = 4 electrons.