1) Al₂O₃→Al₂(SO₄)₃→Al(OH)₃→Al₂O₃
2) Fe₂(SO₄)₃→Fe(OH)₃→Fe₂O₃→Fe₂(SO₄)₃
3) P→P₂O₅→H₃PO₄→Ca₃(PO₄)₂→H₃PO₄→Ca(H₂PO₄)₂
4) SO₃→ZnSO₄→Zn(OH)₂→ZnO

1)Al2O3+3H2SO4=> Al2(SO4)3 + 3H2OAl2(SO4)3+3Ba(OH)2=>3BaSO4 + 2Al(OH)32Al(OH)3=>Al2O3+3H2O2)Fe2(SO4)3+6KOH=>3K2SO4+2Fe(OH)32Fe(OH)3=>Fe2O3+3H2OFe2O3+3H2SO4=>Fe2(SO4)3 + 3H2O3)4P+5O2=>2P2O5P2O5+3H2O=>2H3PO42H3PO4+Ca(OH)2=>Ca(H2PO4)2 + 2H2O