**Werner's Theory of Coordination Compounds**

In 1893, Alfred Werner proposed the coordination theory, which revolutionized the understanding of coordination compounds. According to Werner, coordination compounds are formed by the combination of a central metal ion or atom with surrounding ligands.

**Different Geometrical Shapes**

Werner postulated that coordination compounds can exhibit different geometrical shapes based on the nature and number of ligands attached to the central metal ion. He identified three common geometries for coordination compounds: octahedral, tetrahedral, and square planar.

**Octahedral Geometry**

In octahedral geometry, the central metal ion is surrounded by six ligands arranged at the corners of an octahedron. This geometry is commonly observed in coordination compounds of transition metals. The transition metals have d-orbitals available for bonding, allowing them to form coordination complexes with a coordination number of 6.

**Tetrahedral Geometry**

In tetrahedral geometry, the central metal ion is surrounded by four ligands arranged at the corners of a tetrahedron. This geometry is also commonly observed in coordination compounds of transition metals. However, it is important to note that not all transition metal complexes exhibit tetrahedral geometry. It depends on the nature of the ligands and the oxidation state of the metal ion.

**Square Planar Geometry**

In square planar geometry, the central metal ion is surrounded by four ligands arranged in a square plane. This geometry is predominantly observed in coordination compounds of transition metals with a coordination number of 4. The ligands in square planar complexes usually consist of strong-field ligands that can form strong coordination bonds with the metal ion.

**Coordination Compounds of Transition Metals**

The correct answer to the given question is option 'D' - transition metals. This is because coordination compounds of transition metals are known to exhibit octahedral, tetrahedral, and square planar geometrical shapes, as postulated by Werner. The d-orbitals of transition metals play a crucial role in forming complex structures with different coordination numbers and geometries. The availability of empty d-orbitals allows for the formation of coordination bonds with ligands, resulting in the observed geometrical shapes.

It is worth mentioning that while alkali metals, lanthanides, and actinides can also form coordination compounds, they tend to exhibit different geometries due to the electronic configurations of their outermost energy levels. Therefore, the most common geometries observed in coordination compounds are octahedral, tetrahedral, and square planar, which are predominantly found in coordination compounds of transition metals.