Consider the ions/molecule O2+, O2, O2-, O22-. For increasing bond order the correct option is

🧠 Each additional electron added to the $\ce{O2}$ series goes into the $\pi^*_{2p}$ (antibonding) MO, decreasing bond order by 0.5 per electron.

| Species | Electrons | $\pi^*_{2p}$ filling | BO | |---|---|---|---| | $\ce{O2+}$ | 15 | 1e | (10−5)/2 = 2.5 | | $\ce{O2}$ | 16 | 2e | (10−6)/2 = 2 | | $\ce{O2-}$ | 17 | 3e | (10−7)/2 = 1.5 | | $\ce{O2^{2-}}$ | 18 | 4e | (10−8)/2 = 1 |

Increasing bond order: $\ce{O2^{2-}}$(1) < $\ce{O2-}$(1.5) < $\ce{O2}$(2) < $\ce{O2+}$(2.5)

$\boxed{\text{Answer: (d) } \ce{O2^{2-} < O2^- < O2 < O2^+}}$