If the magnetic moment of a dioxygen species is 1.73 B.M, it may be 

Number of unpaired electrons:

$$\begin{gathered} \mathrm{\mu }=\sqrt{\mathrm{n}(\mathrm{n}+2)} \\ 1.73=\sqrt{\mathrm{n}(\mathrm{n}+2)} \\ \mathrm{n}=1 \end{gathered}$$

Species that has only one unpaired electron, has 1.73 BM.

${\mathrm{O}}_2^{-}$ has 17 electrons:

σ1s²σ∗1s² σ 2s²σ∗2s²σ2p_z​²  π2p_x​²=π2p_y​² π^∗2p_x​²=π^∗2p_y​¹
One unpaired electron

${\mathrm{O}}_2^{+}$ has 15 electrons.

σ1s²σ∗1s² σ 2s²σ∗2s²σ2p_z​²  π2p_x​²=π2p_y​² π^∗2p_x​¹=π^∗2p_y​⁰

One unpaired electron