Na2O:
2 x a = II x 1 => a = I
SO2:
1 x a = II x 2 => a = IV
SO3:
1 x a = II x 3 => a = VI
N2O5:
2 x a = II x 5 => a = V
H2S:
2 x I = 1 x a => a = II
PH3:
1 x a = 3 x I => a = III
P2O5:
2 x a = 5 x II => a = V
Al2O3:
2 x a = 3 x II => a = III
Cu2O:
2 x a = 1 x II => a = I
Fe2O3:
2 x a = 3 x II => a = III
SiO2:
1 x a = 2 x II => a = IV