According to MO theory the bond orders for O$$_2^{2-}$$, CO and NO$$^+$$ respectively, are

The bond order is calculated by:

$$Bond\ Order\ =\ \frac{N_b-N_a}{2}$$

where,

$$N_b$$ is number of bonding electrons

$$N_a$$ is number of antibonding electrons

For,

$$O_2^{2-}$$

Total electrons = 8+8+2 = 18 electrons

MO Electronic Configuration:

$$𝜎_{1s}^2𝜎_{1s}^{*2}𝜎_{2s}^2𝜎_{2s}^{*2}𝜎_{2p_z}^2\left(\pi\ _{2p_x}^2=\pi\ _{2p_y}^2\right)\left(\pi\ _{2p_x}^{*2}=\pi\ _{2p_y}^{*2}\right)$$

Bonding $$N_{b}$$ and Antibonding $$N_{a}$$ electrons: $$N_{b} = 10$$, $$N_{a} = 8$$