Chemical Bonding And Molecular Structure

How many of the following species have the bond order 2? $\mathrm{C}_2, \mathrm{~B}_2^{2-}, \mathrm{N}_2^{2+}, \mathrm{CN}^{+}, \mathrm{NO}^{-}, \mathrm{O}_2, \mathrm{C}_2^{+}$