In which of the following complexes more than one type of structural isomers is possible :

Options

A. `[Co(NH_3)_5(NO_2)]Cl`
B. `[Co(NH_3)_5(H_2O)](NO_2)_3`
C. `[Pt(NH_3)_4 ] Pt (SCN)_4`
D. `[Cr(dmg)_3]`

Explanation

To determine which of the given complexes can exhibit more than one type of structural isomer, we need to analyze the types of structural isomers that can occur in coordination complexes. The main types of structural isomers we will consider are:

1. **Ionization Isomers**: These occur when different ions can be formed upon dissociation of the complex.
2. **Hydrate Isomers**: These involve differences in the number of water molecules coordinated to the metal ion.
3. **Coordinate Isomers**: These occur when there is a difference in the ligands attached to the central metal atom.
4. **Linkage Isomers**: These arise when a ligand can coordinate to the metal through different atoms.

Now, let's analyze each complex provided in the question.

### Step 1: Analyze Complex 1
- **Complex**: [Co(NH3)5Br]SO4
- **Isomers**:
- **Ionization Isomer**: [Co(NH3)5SO4]Br (different free ions)
- **Linkage Isomer**: NO2 can act as ONO, leading to different structures.

**Conclusion**: This complex can exhibit both ionization and linkage isomers.

### Step 2: Analyze Complex 2
- **Complex**: [Co(NH3)5(NO2)]Cl
- **Isomers**:
- **Hydrate Isomer**: [Co(NH3)5Cl]NO2 (water can be replaced)
- **Linkage Isomer**: NO2 can act as ONO.

**Conclusion**: This complex can exhibit both hydrate and linkage isomers.

### Step 3: Analyze Complex 3
- **Complex**: [Cr(NH3)6][Co(CN)6]
- **Isomers**:
- **Linkage Isomer**: SCN can act as NCS.
- **Coordinate Isomer**: The ligands can interchange between the two complexes.

**Conclusion**: This complex can exhibit both linkage and coordinate isomers.

### Step 4: Analyze Complex 4
- **Complex**: [Pt(NH3)4Cl2]
- **Isomers**:
- This complex has only one type of ligand (NH3 and Cl are not interchangeable in a way that would create different structural isomers).

**Conclusion**: This complex cannot exhibit more than one type of structural isomer.

### Final Conclusion
The complexes that can exhibit more than one type of structural isomer are:
- Complex 1: [Co(NH3)5Br]SO4
- Complex 2: [Co(NH3)5(NO2)]Cl
- Complex 3: [Cr(NH3)6][Co(CN)6]

Thus, the answer to the question is that complexes 1, 2, and 3 can exhibit more than one type of structural isomer.