1) 2SO₂ + O₂ = 2SO₃
2) Cu(OH)₂ + 2HCl = CuCl₂ + 2H₂O
3) 4HCl + MnO₂ = MnCl₂ + Cl₂ + 2H₂O
4) 2Al + 6HCl = 2AlCl₃ + 3H₂