JEE Main Chemistry Question (2026) — Solution

Step-by-step solution

Coordination isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex. A. [Ag(NH_3)_2][Ag(CN)_2]: Both the complex cation and anion contain the same metal ion (Ag^+). Interchanging one ligand produces a neutral molecule [Ag(NH_3)(CN)], and interchanging both ligands yields the identical compound. Thus, it does not show coordination isomerism. B. [Co(NH_3)_6][Cr(CN)_6]: The complex contains different metal ions (Co^ 3+ and Cr^ 3+ ). Interchange of ligands gives the coordination isomer [Cr(NH_3)_6][Co(CN)_6]. Thus, it shows coordination isomerism. C. [Co(NH_3)_6][Co(CN)_6]: Both the complex cation and anion contain the same metal ion (Co^ 3+ ). 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(NH_3)_6][Co(CN)_6]: The complex contains different metal ions (Fe^ 3+ and Co^ 3+ ). Interchange of ligands gives the coordination isomer [Co(NH_3)_6][Fe(CN)_6]. Thus, it shows coordination isomerism. E. [Co(NH_3)_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(NH_3)_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