Step 1: The coordination number is determined by counting the number of ligands directly attached to the central metal atom.
Step 2: In \([Co(NH_3)_4Cl_2]Cl\), cobalt is surrounded by four \( NH_3 \) ligands and two \( Cl^- \) ligands, making a total coordination number of 6.
The correct IUPAC name of \([ \text{Pt}(\text{NH}_3)_2\text{Cl}_2 ]^{2+} \) is: