4Al+3O2=>2Al2O3
Al(0)----->Al(+3) se oxidează=>agent reducător
O2(0)----->O3(-2) se reduce=>Ag. oxidant
H2S+3/2O2=>SO2+H2O
S(+2)------>S(+4) se oxidează=>
H2S-Ag.reducator
O2(0)----->O2(-2) se reduce=>Ag.oxidant
P4+5O2=>P4O10
P4(0)------>P4(+5) se oxidează=>Ag. reducător
O2(0)------>O10(-2) se reduce=>Ag. oxidant