Which of the following is non-ionizable?

$\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_3{\mathrm{Cl}}_3\right]$ is non-ionizable.

The complex $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_3{\mathrm{Cl}}_3\right]$ does not have a counter ion present, but all other complexes in the alternatives have at least one counter ion since the molecule that does not have a counter ion will not be ionizable.

Hence, option A is correct.