In which of the following homonuclear diatomic species is the Highest Occupied Molecular Orbital (HOMO) purely -bonding and fully occupied?

Step-by-step solution

Let us write the molecular orbital electronic configuration for the given species to identify their Highest Occupied Molecular Orbital (HOMO). For B₂ (10 electrons): _ 1s ^2 ^*_ 1s ^2 _ 2s ^2 ^*_ 2s ^2 _ 2p_x ^1 = _ 2p_y ^1 . The HOMO is a -bonding orbital but it is not fully occupied (only 2 electrons present in the degenerate pair). For C₂ (12 electrons): _ 1s ^2 ^*_ 1s ^2 _ 2s ^2 ^*_ 2s ^2 _ 2p_x ^2 = _ 2p_y ^2 . The HOMO is purely -bonding and is fully occupied with 4 electrons. For N₂ (14 electrons): _ 1s ^2 ^