Which of the following show maximum bond-order?&

∵$Bond order~\left(BO\right) = \dfrac{{N}_{b} - {N}_{a}}{2}$

Here, ${N}_{b}$~and ${N}_{a}$ are the number of bonding and anti bonding electrons, respectively.

for ${O}_{2}, BO = \dfrac{10 - 6}{2} = 2$

for ${O}_{2}^{-}, BO = \dfrac{10 - 7}{2} = 1 . 5$

for ${O}_{2}^{+}, BO = \dfrac{10 - 5}{2} = 2 . 5$

for ${O}_{2}^{2 -}, BO = \dfrac{10 - 8}{2} = 1$

Hence, maximum value for $BO$ is for ${O}_{2}^{+}$.