In which of the following processes has the bond order increased and paramagnetic character changed to diamagnetic?

🧠 Two conditions must both be satisfied: bond order increases AND paramagnetic → diamagnetic.

🗺️ Analyse each process:

| Process | BO change | Unpaired e⁻ change | Conditions met? | |---------|-----------|-------------------|----------------| | $\mathrm{O_2 \rightarrow O_2^+}$ | 2 → 2.5 ↑ | 2 → 1 (still paramagnetic) | BO ✓, magnetic ✗ | | $\mathrm{NO \rightarrow NO^+}$ | 2.5 → 3 ↑ | 1 → 0 (diamagnetic) | BO ✓, magnetic ✓ | | $\mathrm{O_2 \rightarrow O_2^-}$ | 2 → 1.5 ↓ | 2 → 1 (still paramagnetic) | BO ✗, magnetic ✗ | | $\mathrm{N_2 \rightarrow N_2^+}$ | 3 → 2.5 ↓ | 0 → 1 (becomes paramagnetic) | BO ✗, magnetic ✗ |

⚡ $\mathrm{NO \rightarrow NO^+}$: The lone electron in $\pi^*$ is removed; bond order rises from 2.5 to 3 and the species becomes fully paired (diamagnetic).

$\boxed{\text{Answer: } \mathrm{NO \rightarrow NO^+}}$