Effective atomic number of Co(CO)4is 35, hence it is less stable. It attains stability by
(1) | Oxidation of Co |
(2) | Reduction of Co |
(3) | Dimerization |
(4) | Both (2) & (3) |
To attain the stable atomic number of of a noble gas the complex dimerizes to form Co2(CO)8. It exist in the eqilibrium as :
In this struucture 1 Co-Co bond is equivalent to two Co-CO-Co bonds. This brings the effective atomic number of Co to 78.
Thus, correct option is 3. Dimerization.