Coordination isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex.
A. [Ag(NH3)2][Ag(CN)2]: Both the complex cation and anion contain the same metal ion (Ag+). Interchanging one ligand produces a neutral molecule [Ag(NH3)(CN)], and interchanging both ligands yields the identical compound. Thus, it does not show coordination isomerism.
B. [Co(NH3)6][Cr(CN)6]: The complex contains different metal ions (Co3+ and Cr3+). Interchange of ligands gives the coordination isomer [Cr(NH3)6][Co(CN)6]. Thus, it shows coordination isomerism.
C. [Co(NH3)6][Co(CN)6]: Both the complex cation and anion contain the same metal ion (Co3+). According to the strict definition requiring different metal ions, this is generally excluded from being a primary example of coordination isomerism in standard contexts.
D. [Fe(NH3)6][Co(CN)6]: The complex contains different metal ions (Fe3+ and Co3+). Interchange of ligands gives the coordination isomer [Co(NH3)6][Fe(CN)6]. Thus, it shows coordination isomerism.
E. [Co(NH3)6][Fe(CN)6]: This is the coordination isomer of complex D. Since it contains different metal ions, it also shows coordination isomerism by interchanging ligands to form [Fe(NH3)6][Co(CN)6].
Since complexes D and E are coordination isomers of each other, they must both be included together. Therefore, the complexes that show coordination isomerism are B, D, and E.
Answer: B, D and E Only