Răspuns:
a) 6 H I + 2 H N O 3 → 3 I 2 + 2NO↑+ 4 H 2 O
6 I -I - 6 e - → 6 I 0 (oxidare) agent reducator
2 N V + 6 e - → 2 N II (reducere) agent oxidant
b) H 2 SO 4 + H 2 S → SO 2 + 2 H 2 O + S
S- II - 2 e - → S 0 (oxidare) agent reducator
S- II - 6 e - → S IV (oxidare) agent reducator
S VI + 6 e - → S 0 (reducere) agent oxidant
S VI + 2 e - → S IV (reducere) agent oxidant
c) Pb + Pb O 2 + 2 H 2 S O 4 → 2 PbS O 4 + 2 H 2 O
Pb 0 - 2 e - → Pb II (oxidare) agent reducator
Pb IV + 2 e - → Pb II (reducere) agent oxidant