The correct order of the bond angles of the compounds $\mathrm{SiCl}_4, \mathrm{BF}_3, \mathrm{BeCl}_2$ and $\mathrm{SF}_6$ is

Identify all the species that do not exist $\mathrm{H}_2^{+}, \mathrm{He}_2^{2+}, \mathrm{Li}_2^{2-}, \mathrm{Ne}_2, \mathrm{Be}_2^{-}, \mathrm{He}_2$

The correct pair of species with $(A)$ the highest bond order and ( $B$ ) diamagnetic character is

The incomplete Lewis representation of $\mathrm{CO}_3^{2-}$ is given below. The formal charge on atoms marked as $a, b$ and c respectively, are