Which of the following will have two stereoisomeric forms?
(I) `[Cr(NO_(3))_(3)(NH_(3))_(3)]`
(II) `K_(3)[Fe(C_(2)O_(4))_(3)]`
(III) `[CoCl_(2)(en)_(2)]^(+)`
(IV) `[CoBrCl(o x)_(2)]^(3-)`

Options

A. I only
B. I and II
C. III and IV
D. All of these

Explanation

To determine which of the given coordination compounds will have two stereoisomeric forms, we will analyze each compound based on their geometrical and optical isomerism.

### Step-by-Step Solution:

1. **Identify the Coordination Number and Geometry**:
- For each compound, we first need to identify the central metal ion, its coordination number, and the geometry of the complex.

2. **Analyze Each Compound**:
- **(I) `[Cr(NO3)3(NH3)3]`**:
- This is a coordination complex with chromium as the central metal and has a coordination number of 6 (3 nitrate and 3 ammonia ligands).
- The geometry is octahedral.
- In octahedral complexes with the formula MA3B3, we can have two types of isomers: facial (fac) and meridional (mer).
- **Conclusion**: This complex has **two stereoisomeric forms** (fac and mer).

- **(II) `K3[Fe(C2O4)3]`**:
- This complex has iron as the central metal with a coordination number of 6 (3 oxalate ligands).
- The geometry is octahedral.
- Oxalate is a bidentate ligand, and with three oxalate ligands, this complex can also exhibit optical isomerism.
- **Conclusion**: This complex has **two stereoisomeric forms** (D and L forms).

- **(III) `[CoCl2(en)2]^+`**:
- The central metal is cobalt, with a coordination number of 6 (2 chloride and 2 ethylenediamine ligands).
- The geometry is octahedral.
- This complex can show cis and trans isomerism, and the cis form can also exhibit optical isomerism.
- **Conclusion**: This complex has **three stereoisomeric forms** (cis, trans, and optical isomers).

- **(IV) `[CoBrCl(ox)2]^{3-}`**:
- The central metal is cobalt, with a coordination number of 6 (2 oxalate ligands, 1 bromide, and 1 chloride).
- The geometry is octahedral.
- Similar to the previous case, this complex can show cis and trans isomerism, and the cis form can also exhibit optical isomerism.
- **Conclusion**: This complex has **three stereoisomeric forms** (cis, trans, and optical isomers).

3. **Final Answer**:
- The complexes that have exactly **two stereoisomeric forms** are:
- (I) `[Cr(NO3)3(NH3)3]`
- (II) `K3[Fe(C2O4)3]`
- Therefore, the answer to the question is **(I) and (II)**.