The value of n in the carbonyl is
`[(CO)_(n)-Co-Co-(CO)_(n)]`

Options

A. 4
B. 5
C. 6
D. 8

Explanation

To find the value of \( n \) in the carbonyl compound represented as \([(CO)_{n}-Co-Co-(CO)_{n}]\), we will use the concept of effective atomic number (EAN). The steps are as follows:

### Step 1: Identify the Atomic Number of Cobalt
Cobalt (Co) has an atomic number of 27.

### Step 2: Determine the Nearest Noble Gas Atomic Number
The nearest noble gas to cobalt is Argon (Ar), which has an atomic number of 36.

### Step 3: Write the Effective Atomic Number Formula
The formula for the effective atomic number (EAN) is given by:
\[ \text{EAN} = \text{Atomic Number} - \text{Oxidation State} + \text{Electrons Gained by Coordination} \]

### Step 4: Identify the Oxidation State
In the carbonyl complex, cobalt is in the zero oxidation state because carbonyl ligands (CO) are neutral. Therefore, the oxidation state is 0.

### Step 5: Substitute Known Values into the EAN Formula
Substituting the known values into the EAN formula:
\[ 36 = 27 - 0 + \text{Electrons from CO} \]

### Step 6: Calculate Electrons Gained from CO
Each CO ligand donates 2 electrons. Since there are \( n \) CO ligands, the total contribution from CO ligands is \( 2n \) electrons. Thus, we can rewrite the equation as:
\[ 36 = 27 + 2n \]

### Step 7: Solve for \( n \)
Rearranging the equation gives:
\[ 36 - 27 = 2n \]
\[ 9 = 2n \]
\[ n = \frac{9}{2} = 4.5 \]

### Step 8: Round \( n \) to the Nearest Whole Number
Since \( n \) must be a whole number in this context, we round \( n \) to the nearest whole number, which is 4.

### Conclusion
Thus, the value of \( n \) in the carbonyl complex \([(CO)_{n}-Co-Co-(CO)_{n}]\) is:
\[ \boxed{4} \]

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