The effective atomic number of `Co(CO)_(4)` is 35 and hence is less stable. It attains stability by

Options

A. oxidation of Co
B. reduction of Co
C. dimerization
D. none

Answer

To solve the question regarding the stability of `Co(CO)_(4)` and how it attains stability, we will follow these steps:

### Step 1: Determine the Effective Atomic Number (EAN)
The effective atomic number (EAN) is calculated using the formula:
\[ \text{EAN} = Z + n \]
where \( Z \) is the atomic number of the metal and \( n \) is the number of electrons donated by the ligands.

For cobalt (Co):
- Atomic number \( Z = 27 \)
- In `Co(CO)_(4)`, each CO donates 2 electrons. Therefore, for 4 CO ligands:
\[ n = 4 \times 2 = 8 \]

Thus, the EAN of `Co(CO)_(4)` is:
\[ \text{EAN} = 27 + 8 = 35 \]

### Step 2: Analyze the Stability
The EAN of `Co(CO)_(4)` is 35, which is less than the stable configuration of 36 (the nearest noble gas configuration). This indicates that `Co(CO)_(4)` is less stable.

### Step 3: Determine Ways to Attain Stability
To attain stability, `Co(CO)_(4)` can undergo two processes:

1. **Reduction**:
- If the complex undergoes reduction, it can gain an electron, which would increase the EAN to 36. This can be represented as:
\[ \text{Co(CO)}_4 + e^- \rightarrow \text{Co(CO)}_4^{-1} \]
- This process adds one electron, making the EAN equal to 36.

2. **Dimerization**:
- The complex can also dimerize to form `Co_2(CO)_8`. In this process, two `Co(CO)_(4)` units combine, allowing the CO ligands to share electrons between the two cobalt centers. This can be represented as:
\[ 2 \text{Co(CO)}_4 \rightarrow \text{Co}_2(CO)_8 \]
- In this dimer, the effective atomic number for each cobalt can also reach 36 due to the sharing of electrons through the CO-CO bond.

### Conclusion
Thus, `Co(CO)_(4)` attains stability either through reduction or dimerization.