The species with a bond order of 2.5 with one unpaired electron in sigma bonding molecular orbital is

O2+, O2- and N2-  have an unpaired electron in   π* anti bonding orbital; N2+ has an unpaired  electron in  a σ bonding orbital; N2+-KKσ2s2σ2s*2π2px2π2py2σ2pz1; Bond order=9-42=2.5;