The molecule in which the bond order increases upon addition of an electron
(a)$\mathrm{O}_2$
(b)$\mathrm{B}_2$
(c)$\mathrm{P}_2$
(d)$\mathrm{N}_2$
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
B₂ has half-filled π_u orbitals; adding an electron to a bonding orbital raises the bond order (1 → 1.5). O₂, N₂ and P₂ would add to antibonding orbitals.