(a)Four, $\mu\text{-}\eta^{1}{:}\eta^{1}\text{-}\mathrm{O_2^{2-}}$, blue and diamagnetic.
(b)Five, $\mu\text{-}\eta^{2}{:}\eta^{2}\text{-}\mathrm{O_2^{-}}$, colorless and paramagnetic.
(c)Five, $\mu\text{-}\eta^{2}{:}\eta^{2}\text{-}\mathrm{O_2^{2-}}$, blue and diamagnetic.
(d)Four, $\mu\text{-}\eta^{1}{:}\eta^{1}\text{-}\mathrm{O_2^{-}}$, colorless and paramagnetic.