The valence bond theory is unable to explain the_____

The following figure represents the formation of ____ molecular orbital

The molecular orbital configuration of a diatomic molecule is 

${\text{σ1s}}^{\text{2}}{\text{ σ*1s}}^{\text{2}}{\text{ σ2s}}^{\text{2}}{\text{ σ*2s}}^{\text{2}}{{\text{ σ2p}}_{\text{x}}}^{\text{2}}{{\text{ π2p}}_{\text{y}}}^{\text{2}}{{\text{ π2p}}_{\text{z}}}^{\text{2}}$

Its bond order is ____