If the magnetic moment of a di-oxygen species is 1.73 BM, it may be

🧠 $\mu = 1.73$ BM (spin-only) → $\sqrt{n(n+2)} = 1.73$ → $n(n+2) = 3$ → $n = 1$ unpaired electron. Find which $\ce{O2}$ species have exactly 1 unpaired electron.

| Species | e | $\pi^*_{2p}$ electrons | Unpaired | |---|---|---|---| | $\ce{O2}$ | 16 | 2 (one in each degenerate MO) | 2 ✗ | | $\ce{O2+}$ | 15 | 1 | 1 ✓ | | $\ce{O2-}$ | 17 | 3 (one full + one half) | 1 ✓ | | $\ce{O2^{2-}}$ | 18 | 4 (both full) | 0 ✗ |

Both $\ce{O2+}$ and $\ce{O2-}$ have exactly 1 unpaired electron → $\mu = 1.73$ BM.

$\boxed{\text{Answer: (a) } \ce{O2-}\text{ or }\ce{O2+}}$