In the complex `[CoCl_(2)(en)_(2)]Br`, the co-ordination number and oxidation state of cobalt are :

Options

A. 6 and +3
B. 3 and +3
C. 4 and +2
D. 6 and +1

Answer

To determine the coordination number and oxidation state of cobalt in the complex \([CoCl_2(en)_2]Br\), we can follow these steps:

### Step 1: Identify the ligands and their denticity
- The complex contains two types of ligands: chloride ions (\(Cl^-\)) and ethylenediamine (en).
- Chloride (\(Cl^-\)) is a monodentate ligand, meaning it can form one bond with the metal.
- Ethylenediamine (en) is a bidentate ligand, meaning it can form two bonds with the metal.

### Step 2: Calculate the coordination number
- The coordination number is the total number of bonds formed between the metal and the ligands.
- There are 2 chloride ions contributing 2 to the coordination number (1 from each \(Cl^-\)).
- There are 2 ethylenediamine ligands, and since each can bind twice, they contribute 4 to the coordination number (2 from each en).
- Therefore, the total coordination number is:
\[ \text{Coordination Number} = 2 \, (from \, Cl) + 4 \, (from \, en) = 6 \]

### Step 3: Determine the oxidation state of cobalt
- Let the oxidation state of cobalt be \(x\).
- The charges from the ligands must be considered:
- Each \(Cl^-\) contributes \(-1\), and there are 2 of them, contributing \(-2\).
- Ethylenediamine (en) is a neutral ligand, contributing \(0\).
- The bromide ion (\(Br^-\)) outside the coordination sphere contributes \(-1\).
- The overall charge of the complex is neutral, so we can set up the equation:
\[ x + 2(-1) + 0 + (-1) = 0 \]
Simplifying this gives:
\[ x - 2 - 1 = 0 \implies x - 3 = 0 \implies x = +3 \]

### Conclusion
- The coordination number of cobalt in the complex \([CoCl_2(en)_2]Br\) is **6**.
- The oxidation state of cobalt is **+3**.

### Final Answer:
- Coordination Number: 6
- Oxidation State of Cobalt: +3

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