Chemistry - Coordination Chemistry Question with Solution | TestHub

The correct pair is D. Linkage isomerism occurs when a ligand can bind to the central metal atom through different donor atoms. In option D, the nitrite ligand ($N{O}_2^{-}$) can bind via nitrogen (nitro, $-N{O}_2$) or oxygen (nitrito, $-ONO$), forming linkage isomers.

Explanation for other options:

A. These are coordination isomers, but the given pair is not correctly matched as the ligands are exchanged between the cationic and anionic parts.

B. These are linkage isomers, but the formula for the second complex is incorrect. It should be $[Co(en{)}_2(ONO{)}_2{]}^{-}$.

C. These are coordination isomers, but the given pair is not correctly matched. The first complex is a square planar complex, while the second pair represents coordination isomers where ligands are exchanged between cationic and anionic complexes.