Which type of isomerism is shown by the  complex compounds?

\([Co(NH_3)_3Br]SO_4\) and \([Co(NH_3)_3]SO_4\)

Coordination isomerism

The correct answer is option 3. Coordination isomerism.

Coordination isomerism occurs in coordination compounds when there are different ligands coordinated to the central metal ion, resulting in isomers with the same molecular formula but different arrangements of ligands around the metal center.

Let's consider the two complex compounds provided:

\([Co(NH_3)_3Br]SO_4\): In this compound, the cobalt ion (\(Co\)) is coordinated to three ammonia ligands (\(NH_3\)) and one bromine ligand (\(Br\)).

\([Co(NH_3)_3]SO_4\): In this compound, the cobalt ion (\(Co\)) is coordinated to only three ammonia ligands (\(NH_3\)).

Although both compounds have the same overall formula (\(Co(NH_3)_3X\) where \(X\) is a ligand), they are coordination isomers because they differ in the arrangement of ligands around the central cobalt ion. In one compound, there is a bromine ligand present, while in the other, there is no additional ligand beyond the three ammonia ligands.

This difference in the coordination sphere results in distinct chemical and physical properties between the isomers. Coordination isomerism is one of the several types of isomerism observed in coordination compounds, where the isomers have different structures but the same composition.