Which of the following reactions are redox reactions? Check all that apply. a) (4Li(s) + O₂(g) arrow 2Li₂O(s)) b) (Mg(s) + Fe2+(aq) arrow Mg2+(aq) + Fe(s)) c) (Pb(NO₃)(aq) + Na₂SO₄(aq) arrow PbSO₄(s) + 2NaN)