In the coordination compound `[Co(en)_2Cl_2]Cl` (en=ethylenediamine), the coordination number and oxidation number of the central atom are, respectively:

Options

A. (a) 4, +3
B. (b) 6, +2
C. (c) 4, +2
D. (d) 6, +3

Explanation

To determine the coordination number and oxidation number of the central atom in the coordination compound \([Co(en)_2Cl_2]Cl\), we can follow these steps:

### Step 1: Identify the Ligands
The ligands in the compound are:
- Ethylenediamine (en), which is a bidentate ligand (it can donate two pairs of electrons).
- Chloride ions (Cl⁻), which are monodentate ligands (they can donate one pair of electrons).

### Step 2: Determine the Coordination Number
The coordination number is defined as the total number of donor atoms that are bonded to the central metal atom (Co in this case).

- Each ethylenediamine (en) ligand donates 2 pairs of electrons, contributing 2 donor atoms per ligand. Since there are 2 ethylenediamine ligands, they contribute:
\[ 2 \, \text{(from en)} \times 2 \, \text{(number of en ligands)} = 4 \, \text{donor atoms} \]

- Each chloride ion (Cl⁻) donates 1 pair of electrons. Since there are 2 chloride ions, they contribute:
\[ 1 \, \text{(from Cl⁻)} \times 2 \, \text{(number of Cl⁻ ligands)} = 2 \, \text{donor atoms} \]

- Therefore, the total coordination number is:
\[ 4 \, \text{(from en)} + 2 \, \text{(from Cl⁻)} = 6 \]

### Step 3: Calculate the Oxidation Number
Next, we need to find the oxidation number of the central metal atom (Co).

- Let the oxidation number of Co be \(x\).
- The ethylenediamine (en) is a neutral ligand, contributing 0 to the charge.
- Each chloride ion (Cl⁻) has a charge of -1, and there are 2 of them, contributing a total of -2 to the charge.
- The overall charge of the complex \([Co(en)_2Cl_2]^+\) is +1 (since it is balanced by the Cl⁻ outside the brackets).

Setting up the equation:
\[ x + 0 - 1 \times 2 = +1 \]
\[ x - 2 = +1 \]
\[ x = +3 \]

### Final Answer
- Coordination Number: **6**
- Oxidation Number: **+3**