What is the effective atomic number $(EAN)$ of $Zn$ in $[Zn(NH_3)_4]SO_4$? (Atomic number of $Zn = 30$)

The effective atomic number $(EAN)$ of $Co(CO)_4$ is $35$,which makes it less stable. It attains stability by:

$EAN$ of complex $[Fe(C_2O_4)_3]^{3-}$ is

For the complex $Cr(CO)_x$,find the value of $x$?

What is the value of the effective atomic number $(EAN)$ of cobalt in the $[Co(NH_3)_6]^{3+}$ complex,given that the atomic number of $Co$ is $Z=27$?

Which one of the following does not follow Sidgwick $EAN$ rule?