In `[Co(NH_3)_4 Cl_2]Cl` the co-ordination number of cobalt is-

Options

A. 4
B. 6
C. 2
D. 7

Answer

To determine the coordination number of cobalt in the complex `[Co(NH₃)₄Cl₂]Cl`, we can follow these steps:

### Step 1: Identify the Components of the Complex
The complex is `[Co(NH₃)₄Cl₂]Cl`. Here, we have:
- Cobalt (Co) as the central metal atom.
- Four ammonia (NH₃) molecules as ligands.
- Two chloride (Cl) ions as ligands.
- An additional chloride ion outside the coordination sphere.

### Step 2: Understand Coordination Number
The coordination number is defined as the total number of ligand donor atoms that are bonded to the central metal atom. Each ligand can donate one or more pairs of electrons to the metal.

### Step 3: Analyze the Ligands
- **Ammonia (NH₃)**: Each ammonia molecule is a monodentate ligand, meaning it can donate one pair of electrons to the cobalt ion. Since there are four NH₃ molecules, they contribute:
- 4 NH₃ × 1 pair = 4 pairs of electrons.

- **Chloride (Cl)**: Each chloride ion is also a monodentate ligand. There are two chloride ions, which contribute:
- 2 Cl × 1 pair = 2 pairs of electrons.

### Step 4: Calculate Total Coordination Number
Now, we add the contributions from both types of ligands:
- Total pairs from NH₃ = 4
- Total pairs from Cl = 2
- Total coordination number = 4 + 2 = 6

### Conclusion
The coordination number of cobalt in the complex `[Co(NH₃)₄Cl₂]Cl` is **6**.

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