Răspuns:
2 H N O3 + 3H2S => 3S+ 2 NO + 4 H20
3 S -II - 6 e - => 3 S 0 (oxidare) agent reducator
2 N V + 6 e - => 2 N II (reducere) agent oxidant
4 Fe + 3O2 => 2 Fe1O3
4 Fe 0 - 12 e - => 4 Fe III (oxidare) agent reducator
6 O 0 + 12 e - => 6 O -II (reducere) agent oxidant
2H2S + H2SO3 => 3 S + 3H2O
2 S -II - 4 e - => 2 S 0 (oxidare) agent reducator
S IV + 4 e - => S 0 (reducere) agent oxidant