Which of the following is a polynuclear compound
 

Complex in which two central metal atoms are present is called poly nuclear complexes.

$\left[{\left(\mathrm{Co}\right)}_2{\left({\mathrm{NH}}_3\right)}_6{\left(\mathrm{OH}\right)}_3\right]{\mathrm{Cl}}_3$ is a polynuclear  because it has more than one metal in the complex