Which of the following complexes exists in facial and meridional forms?

Options

A. a) `[Co("dien)_(3)]^(3+)`
B. b) `[Co(NH_(3))_(3)Cl_(3)]`
C. c) `[Co("en")_(3)]^(3+)`
D. d) `[Co("gly")_(3)]`

Explanation

To determine which of the given complexes exists in both facial (fac) and meridional (mer) forms, we need to follow a systematic approach:

### Step-by-Step Solution:

1. **Understanding Isomerism**:
- **Facial (fac) Isomer**: In this form, three identical ligands occupy one face of an octahedron, meaning that any two identical ligands are adjacent to each other.
- **Meridional (mer) Isomer**: In this form, three ligands and the metal are in one plane. This means that the three identical ligands are arranged in such a way that they form a plane with the metal.

2. **Identifying the Complex Formula**:
- For a complex to exhibit both fac and mer isomers, it must have the general formula of the form \( M(A_3B_3) \), where \( M \) is the metal, \( A \) is one type of ligand, and \( B \) is another type of ligand. This ensures that there are three of each type of ligand.

3. **Analyzing the Given Options**:
- We need to analyze the complexes provided in the question to see which one fits the \( M(A_3B_3) \) formula.

4. **Checking Each Option**:
- **Option A**: This complex does not fit the required formula.
- **Option B**: Cobalt complex with \( NH_3 \) and \( Cl \) ligands fits the \( M(A_3B_3) \) formula, as it has three \( NH_3 \) ligands and three \( Cl \) ligands.
- **Option C**: This complex does not fit the required formula.
- **Option D**: This complex does not fit the required formula.

5. **Conclusion**:
- The only complex that exists in both facial and meridional forms is **Option B: \( Co(NH_3)_3Cl_3 \)**.

### Final Answer:
The complex that exists in both facial and meridional forms is **Option B: \( Co(NH_3)_3Cl_3 \)**.

---