The isomer(s) of $\left[\mathrm{C}\mathrm{o}{\left(\mathrm{N}{\mathrm{H}}_3\right)}_4\mathrm{C}{\mathrm{l}}_2\right.]$ that has/ have a $\mathrm{C}\mathrm{l}-\mathrm{C}\mathrm{o}-\mathrm{C}\mathrm{l}$ angle of ${90}^{\mathrm{o}},$ is the cis-isomer only. The structure of the cis isomers is written below:

Here, as we can see that one ${90}^{\mathrm{o}}$ angle of $\mathrm{Cl}-\mathrm{Co}-\mathrm{Cl}$ bond is present.