Which of the following elements would have the lowest oxidation number?

Magnesium, the element, is produced commercially by electrolysis from a molten salt (the 'electrolyte') using a cell similar to the one shown here. (a) What is the most common oxidation number for Mg when it is part of a salt?

For each of the following balanced oxidation–reduction reactions, (i) identify the oxidation numbers for all the elements in the reactants and products and (ii) state the total number of electrons transferred in each reaction. (a) I₂O₅(s) + 5 CO(g) → I₂(s) + 5 CO₂(g) (b) 2 Hg²⁺(aq) + N₂H₄(aq) → 2 Hg(l) + N₂(g) + 4 H⁺(aq) (c) 3 H₂S(aq) + 2 H⁺(aq) + 2 NO₃^-(aq) → 3 S(s) + 2 NO(g) + 4 H₂O(l)