Practice question

For Be₂ : (sigma 1s)² (sigma^* 1s)² (sigma 2s)² (sigma^* 2s)² . Bonding = 4, antibonding = 4. Bond order = (4 - 4/2) = 0 , but Li₂ (bond order 1) is stable. Adjusting for intent: Be₂ is typically unstable despite theoretical 1 in some excited states; He₂⁺ fits better with bond order 0.5. Correcting: H₂⁻ has bond order 0.5, unstable in neutral context.