What is effective atomic number of cobalt in \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}\) if \(\operatorname{Co}(Z=27) ?\)

The total number of electrons present with a central metal atom or ion in a coordination complex plus the electrons donated by the ligands is known as Effective Atomic Number (EAN).
The formula to calculate the EAN is as follows.
Effective atomic number \(=\mathrm{Z}-\mathrm{O} . \mathrm{N}+2 \mathrm{C} . \mathrm{N}\)
\(\mathrm{Z}=\) Atomic number
O.N= Oxidation number
C. \(\mathrm{N}=\) Coordination number
\(
\begin{aligned}
& {\left[\mathrm{C}_0\left(\mathrm{NH}_3\right)_6\right]^{3+} \quad \mathrm{C}_0^{3+}} \\
& \mathrm{Z}=27 . \mathrm{O} \cdot \mathrm{N} .=3 . \quad \text { C.N. }=6 \\
& \mathrm{EAN}=27-3+2 \times 6=36
\end{aligned}
\)