What is the Effective atomic number of Fe in Fe2(CO)9?

35 36 37 Cannot be calculated

35

Effective Atomic Number $=$ Atomic number of central atoms $-$ (oxidation no. of central atom) $+$ No. of electron taken from Ligands. Atomic No. of $Fe=26$ and ′CO′ is a neutral ligand. So, oxidation no. of central atom $=0$. The $3$ terminal bonds for each ′Fe′ share $2$ electrons each while the middle common bonds share $1$ electron.  Total shared electrons $=3\times 2+3=9$ Now, $EAN=26-0+9=35$