Which of the following statements is incorrect for the following species:

${\mathrm{BO}}_3^{3-}, {\mathrm{CO}}_3^{2-}, {\mathrm{NO}}_3^{-}$

The total number of electrons present in ${\mathrm{BO}}_3^{3-}$ is 33, in ${\mathrm{CO}}_3^{2-}$ is 33, and in ${\mathrm{NO}}_3^{-}$is 33. Therefore, the given species are isoelectronic and isostructural because all have trigonal planar structure.

Resonating structures of ${\mathrm{CO}}_3^{2-}$ are shown below, in which one structure, there are 2 bonds between C and O whereas, in the rest of the two structures, there are single bonds between C and O. 

The average bond order of  ${\mathrm{CO}}_3^{2-}$is:

$\begin{array}{ccc}\mathrm{Bond} \mathrm{order}& =& \frac{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{bonds}}{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{resonating} \mathrm{structures}}\\ & =& \frac{4}{3}\\ & =& 1.33\end{array}$

Resonating structures of ${\mathrm{NO}}_3^{-}$ are shown below , in which there is one structure, there is 2 bonds between N and O whereas in the rest of the two structures, there are single bonds between N and O.

 Average bond order of ${\mathrm{NO}}_3^{-}.$

$\begin{array}{ccc}\mathrm{Bond} \mathrm{order}& =& \frac{4}{3}\\ & =& 1.33\end{array}$

It seems that the bond order of borate ion, ${\mathrm{BO}}_3^{3-}$ is 1 but boron is electron-deficient and has a vacant 2p_z orbital. So, one oxygen atom shares its lone pair with the vacant 2p_z orbital of boron. As there are 3 oxygen atoms in the borate ion, thereby three back bonding is possible. 

Therefore, the bond order of the borate ion is:

$\begin{array}{ccc}\mathrm{Bond} \mathrm{order}& =& \frac{4}{3}\\ & =& 1.33\end{array}$

Hybridization of C in ${\mathrm{CO}}_3^{2-}$, N in ${\mathrm{NO}}_3^{-}$, and B in ${\mathrm{BO}}_3^{3-}$ is sp² and has nearly a $120°$ bond angle.