The co-ordination number of cobalt in the complex `[Co(en)_2Br_2]Cl_2` is

Options

A. (a) `2`
B. (b) `6`
C. (c) `5`
D. (d) `4`

Explanation

To determine the coordination number of cobalt in the complex \([Co(en)_2Br_2]Cl_2\), we will analyze the ligands attached to the cobalt ion.

### Step-by-Step Solution:

1. **Identify the central metal atom**:
The central metal atom in the complex is cobalt (Co).

2. **Identify the ligands**:
The ligands in the complex are:
- \(en\) (ethylenediamine), which is a bidentate ligand.
- \(Br\) (bromide), which is a monodentate ligand.

3. **Determine the contribution of each ligand to the coordination number**:
- Each \(en\) ligand can bind to the cobalt through two donor atoms (nitrogen atoms). Since there are 2 \(en\) ligands, they contribute:
\[ 2 \, \text{(from one } en\text{)} \times 2 \, \text{(number of } en\text{ ligands)} = 4 \]
- Each \(Br\) ligand can bind through one donor atom. Since there are 2 \(Br\) ligands, they contribute:
\[ 1 \, \text{(from one } Br\text{)} \times 2 \, \text{(number of } Br\text{ ligands)} = 2 \]

4. **Calculate the total coordination number**:
Now, we add the contributions from both types of ligands:
\[ \text{Total coordination number} = 4 \, \text{(from } en\text{)} + 2 \, \text{(from } Br\text{)} = 6 \]

5. **Conclusion**:
The coordination number of cobalt in the complex \([Co(en)_2Br_2]Cl_2\) is 6.

### Final Answer:
The coordination number of cobalt in the complex \([Co(en)_2Br_2]Cl_2\) is **6**.