The B2 2- orbital is a molecular orbital formed by the combination of two atomic orbitals from two boron atoms. It is derived from the overlap of two 2p atomic orbitals. The B2 2- orbital can be represented by a molecular orbital diagram, where the two 2p orbitals combine to form two molecular orbitals: a bonding orbital (lower in energy) and an antibonding orbital (higher in energy).
In the B2 2- orbital picture, the bonding orbital is lower in energy and has a lower electron density in the internuclear region. It contributes to the stability of the molecule. The antibonding orbital is higher in energy and has a node in the internuclear region. It does not contribute to the stability of the molecule and is less populated with electrons.
The B2 2- orbital diagram would show the relative energy levels of the atomic orbitals and the resulting molecular orbitals. The bonding orbital would be lower in energy and occupied by electrons, while the antibonding orbital would be higher in energy and unoccupied or less populated with electrons.