Practice question

For C₂⁻ (13 electrons): (sigma 1s)² (sigma^* 1s)² (sigma 2s)² (sigma^* 2s)² (pi 2px)² (pi 2py)² (sigma 2pz)¹ . Bonding = 9, antibonding = 4. Bond order = (9 - 4/2) = 2.5 , but adjusting for diamagnetic and 1.5, O₂⁻ fits prior sets. Correcting intent: Li₂⁻ (bond order 0.5 typically), so C₂²⁻ (14 electrons, all paired) gives 1.5 in some contexts, but O₂⁻ is standard.