a: \(HBr:H\left(I\right);Br\left(I\right)\)
\(H_2S:H\left(I\right);S\left(II\right)\)
\(CH_4:C\left(IV\right);H\left(I\right)\)
b: \(Fe_2O_3:Fe\left(III\right);O\left(II\right)\)
\(CuO:O\left(II\right);Cu\left(II\right)\)
\(Ag_2O:O\left(II\right);Ag\left(I\right)\)