A pair of molecules with see-saw shape and linear shape, respectively, is

How many ions of the following have a bond order of  $2.5 ?$ 

${\mathrm{N}}_2^{-};{\mathrm{NO}}^{-};{\mathrm{C}}_2^{-};{\mathrm{N}}_2^{+};{\mathrm{C}}_2^{2-};{\mathrm{CN}}^{+}$