1) S→SO₂→Na₂SO₃→SO₂; S+O₂=SO₂; SO₂+2NaOH=Na₂SO₃+H₂O; Na₂SO₃+2HCl=SO₂+2NaCl+H₂; 2) Mg→MgO→MgSO₄→Mg(OH)₂; 2Mg+O₂=2MgO; MgO+Na₂SO₄=MgSO₄+Na₂O; MgSO₄+2KOH=Mg(OH)₂+K₂SO₄.