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

Choose the correct option regarding the following complex compounds which follow $(F)$ and do not follow $(NF)$ the Sidgwick $EAN$ rule:
$I. [(Ph_3P)_2PdCl_2PdCl_2]$
$II. [NiBrCl(en)]$
$III. Na_4[Fe(CN)_5NOS]$
$IV. Cr(CO)_3(NO)_2$
$I-II-III-IV$

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

Which of the following complex compounds/ions obeys the Sidgwick $EAN$ rule?

What is the $EAN$ of nickel in $Ni(CO)_4$?

In $K_4[Fe(CN)_6]$,the $E.A.N.$ of $Fe$ is