Identify the species having one$\mathrm{\pi }$ -bond and maximum number of canonical forms from the following:

$$\begin{gathered} \text{ Among }{\mathrm{SO}}_3,{\mathrm{O}}_2,{\mathrm{SO}}_2\text{ and }{\mathrm{CO}}_3^{-2},O_2 \\ \text{only }{\mathrm{CO}}_3^{2\cdot }\text{ has only one }\pi \text{-bond } \end{gathered}$$

${\mathrm{CO}}_3^{2-}$ has maximum number of canonical form

Hence, correct option is: (A)${\mathrm{CO}}_3^{2-}$