The oxidation state of cobalt in the complex compound `[Co(NH_3)_6]Cl_3` is

Options

A. (a) `+3`
B. (b) `+6`
C. (c) `+5`
D. (d) `+2`

Explanation

To determine the oxidation state of cobalt in the complex compound \([Co(NH_3)_6]Cl_3\), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the components of the complex**: The complex \([Co(NH_3)_6]Cl_3\) consists of a cobalt ion surrounded by six ammonia ligands and three chloride ions outside the coordination sphere.

2. **Understand the charges**: Ammonia (\(NH_3\)) is a neutral ligand, meaning it does not contribute any charge. The chloride ions (\(Cl^-\)) each have a charge of -1. Since there are three chloride ions, their total contribution to the charge is -3.

3. **Set up the equation for oxidation state**: Let the oxidation state of cobalt be \(x\). The overall charge of the complex ion \([Co(NH_3)_6]^{3+}\) can be expressed as:
\[ x + 6(0) = +3 \]
Here, \(6(0)\) represents the contribution from the six ammonia ligands.

4. **Account for the charge from chloride ions**: Since there are three chloride ions contributing a total charge of -3, we can express the overall charge of the compound as:
\[ [Co(NH_3)_6]^{3+} + 3Cl^- = 0 \]

5. **Solve for \(x\)**: From the equation \(x + 0 = +3\), we can solve for \(x\):
\[ x = +3 \]

6. **Conclusion**: The oxidation state of cobalt in the complex \([Co(NH_3)_6]Cl_3\) is +3.

### Final Answer:
The oxidation state of cobalt in the complex compound \([Co(NH_3)_6]Cl_3\) is +3.