Step 1: Fix the naming recipe: alphabetical ligand order, -o ending for negative ligands, neutral ligand names as they are, metal oxidation state in brackets, and for any anionic complex add -ate to the metal.
(i) In \( [Cr(NH_3)_2Cl_2(en)]Cl \) the counter chloride sitting outside tells us the coordination sphere carries \( +1 \). Balancing \( Cr \) against two neutral ammines, two \( -1 \) chlorides and neutral en gives chromium as \( +3 \). Listing ligands a to z (ammine, chlorido, ethanediamine) and enclosing the substituted-name ligand en in brackets yields diamminedichlorido(ethane-1,2-diamine)chromium(III) chloride.
(ii) \( [Pt(NH_3)_4Cl_2][PtCl_4] \) is a salt of two complex ions. The cation is \( [Pt(NH_3)_4Cl_2]^{2+} \), which needs platinum \( +4 \); the anion is \( [PtCl_4]^{2-} \), which needs platinum \( +2 \). Naming the positive ion first and then the negative ion (metal ending changed to platinate) gives tetraamminedichloridoplatinum(IV) tetrachloridoplatinate(II).
Step 2: Both names are checked to make sure ligand counts (di, tetra) and oxidation numbers match the formulas.