In h2-, how many electrons occupy the mo shown?

Atomic number of H = 1

Valence electron configuration = 1s¹

When 2 H atoms combine, two 1s orbitals overlap resulting in the formation of a sigma bond.

H₂ Molecular configuration = σ1s²

In H₂⁻ there is an addition of 1 electron which goes to occupy the σ * antibonding orbital:

H₂⁻ = σ1s² σ*1s¹

Thus, 3 electrons will occupy the MO of H2⁻ in which:

2 electrons are bonding

1 electron antibonding