Isomers are two or more compounds that have the same chemical formula but a different arrangement of atoms. Because of the different arrangement of atoms, they differ in one or more physical or chemical properties. Two principal types of isomerism are known among coordination compounds. Each of which can be further subdivided.

(a) Stereoisomerism

(i) Geometrical isomerism (ii) Optical isomerism

(b) Structural isomerism

(i) Linkage isomerism

(ii) Coordination isomerism

(iii) Ionisation isomerism

(iv) Solvate isomerism

Stereoisomers have the same chemical formula and chemical bonds, but they have different spatial arrangement. Structural isomers have different bonds.

Which of the following ligand cannot show linkage isomerism?

H₂O

H₂O ligand cannot show linkage isomerism as it has only one oxygen donor atom i.e., monodentate ligand.