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

The compound with more covalent character in the following is

What is the correct order of bond lengths in the following molecules?

I. $\mathrm{O}_2$

II. $\mathrm{O}_2^{+}$

III. $\mathrm{O}_2^{-}$

IV. $\mathrm{O}_2^{2-}$

Which one of the following compound is hypervalent?