Question

An effective atomic number of $Co(C{O_4})$ is 35 and hence it is less stable. It attains stability by
A. Oxidation of Co
B. Reduction of Co
C. Dimerization
D. Both B and C

Answer 1

In the complex $Co(C{O_4})$, the central metal atom cobalt is surrounded by four carbon monoxide molecules. The electrons shared by cobalt is 27 and electrons shared by four carbon monoxide atoms is 8 which makes 35 electrons. To fully fill the rule it should gain electrons from the other atoms.

Complete answer:
The effective atomic number (EAN) number shows the total number of electrons surrounding the nucleus of the central metal atom in a complex. The EAN number is the combination of electrons of metal atoms and electrons of surrounding electrons donating ligands or atoms.
The English chemist named Nevil.V.Sidwick based on his observation gave a rule known as EAN rule. It says that in a metal complex, the metal atom tends to surround itself by surrounding sufficiently by atoms or molecules that the effective atomic number should be equal to the atomic number of the stable noble gas element which is located at the same period as the metal.
The given complex is $Co(C{O_4})$, The effective atomic number of this complex is 35, 27 electrons of cobalt and 8 electrons of four carbon monoxide. To attain the stability, the value of effective atomic number should be 36 which is the atomic number of noble gas krypton present in the same period as the cobalt.
To attain the stability the metal atom of complex $Co(C{O_4})$ will undergo reduction or dimerization.
Therefore, the correct option is D.

Note: EAN rule is also known as 18-electron rule. The EAN rule helps to know the number of ligands present in the complex and also the product formed from their reactions.