As $\mathrm{C}\mathrm{o}\mathrm{C}{\mathrm{l}}_3.3\mathrm{N}{\mathrm{H}}_3$ is represented as $\left[\mathrm{C}\mathrm{o}\right(\mathrm{N}{\mathrm{H}}_3{)}_3\mathrm{C}{\mathrm{l}}_3]$ it means it does not have any ionisable $\mathrm{C}{\mathrm{l}}^{-}$ hence no white ppt of AgCl is possible. In other three complexes given here ionisable $\mathrm{C}{\mathrm{l}}^{-}$ is possible so white ppt of AgCl is possible.
$\left[\mathrm{C}\mathrm{o}\right(\mathrm{N}{\mathrm{H}}_3{)}_3\mathrm{C}{\mathrm{l}}_3]\stackrel{\mathrm{A}\mathrm{g}\mathrm{N}{\mathrm{O}}_3}{\to }$ no ppt