In which of the following processes does the bond order increase and paramagnetic character change to diamagnetic?

🧠 Two conditions must both be satisfied: (i) bond order increases, (ii) magnetic character changes from paramagnetic to diamagnetic.

| Process | BO change | Magnetic change | |---|---|---| | $\ce{O2 -> O2+}$ | 2 → 2.5 ↑ | paramagnetic → paramagnetic (still 1 unpaired e) ✗ | | $\ce{O2 -> O2^{2-}}$ | 2 → 1 ↓ | paramagnetic → diamagnetic, but BO decreases ✗ | | $\ce{NO -> NO+}$ | 2.5 → 3 ↑ ✓ | paramagnetic → diamagnetic ✓ | | $\ce{N2 -> N2+}$ | 3 → 2.5 ↓ | diamagnetic → paramagnetic ✗ |

🗺️ NO (15e) has 1 unpaired electron in $\pi^*_{2p}$ → paramagnetic. $\ce{NO+}$ (14e, isoelectronic with $\ce{N2}$) has all electrons paired → diamagnetic. Bond order 2.5 → 3 ✓.

$\boxed{\text{Answer: (c) } \ce{NO -> NO+}}$