Which of the following isomerism is not possible for complexes having molecular formulae?
(I) `Pt(SCN)_(2)*3PE t_(3)`,
(II) `CoBr*SO_(4)*5NH_(3)`
(III) `FeCl_(2)*6H_(2)O`

Options

A. Optical
B. Linkage
C. Ionisation
D. Hydrate

Explanation

To determine which type of isomerism is not possible for the given coordination complexes, we will analyze each complex one by one. The types of isomerism we will consider are linkage isomerism, ionization isomerism, hydrate isomerism, and optical isomerism.

### Step 1: Analyze the first complex `Pt(SCN)₂·3PEt₃`
- **Linkage Isomerism**: The thioscyanate (SCN⁻) ligand can coordinate through either the sulfur (S) or the nitrogen (N) atom. This means that linkage isomerism is possible for this complex.
- **Ionization Isomerism**: This complex does not contain any counter ions that can be exchanged with the ligands, so ionization isomerism is not applicable.
- **Optical Isomerism**: Since the complex is symmetrical and does not have a chiral center, optical isomerism is not possible.

### Step 2: Analyze the second complex `CoBr·SO₄·5NH₃`
- **Linkage Isomerism**: There are no ambidentate ligands present in this complex, so linkage isomerism is not applicable.
- **Ionization Isomerism**: This complex can show ionization isomerism because the bromide (Br⁻) and sulfate (SO₄²⁻) can be exchanged. For example, one isomer can have Br⁻ outside the coordination sphere while another can have SO₄²⁻ outside.
- **Optical Isomerism**: This complex can exhibit optical isomerism if it is chiral, which is possible depending on the arrangement of the ligands.

### Step 3: Analyze the third complex `FeCl₂·6H₂O`
- **Linkage Isomerism**: There are no ambidentate ligands in this complex, so linkage isomerism is not applicable.
- **Ionization Isomerism**: This complex can show ionization isomerism as it can release different ions upon dissociation.
- **Optical Isomerism**: This complex can exhibit optical isomerism if it is chiral, which is not possible here as the arrangement is symmetrical.

### Conclusion
Based on the analysis:
- **For `Pt(SCN)₂·3PEt₃`**: Linkage isomerism is possible, but optical isomerism is not.
- **For `CoBr·SO₄·5NH₃`**: Linkage isomerism is not possible, but ionization and optical isomerism are possible.
- **For `FeCl₂·6H₂O`**: Linkage isomerism is not possible, but ionization and optical isomerism are possible.

The type of isomerism that is not possible for the complexes is **linkage isomerism** for the second and third complexes.

### Final Answer
The isomerism that is not possible for the complexes is **linkage isomerism**.