The $EAN$ of the central metal atom in $Fe_2(CO)_9$ is:

Among $V(CO)_6$,$Cr(CO)_5$,$Cu(CO)_3$,$Mn(CO)_5$,$Fe(CO)_5$,$[Co(CO)_3]^{3-}$,$[Cr(CO)_4]^{4-}$,and $Ir(CO)_3$,the total number of species isoelectronic with $Ni(CO)_4$ is. . . . . [Given atomic number : $V=23$,$Cr=24$,$Mn=25$,$Fe=26$,$Co=27$,$Ni=28$,$Cu=29$,$Ir=77$ ]

Which of the following coordination complexes is an exception to the $EAN$ rule? (Given atomic numbers: $Pt = 78, Fe = 26, Zn = 30, Cu = 29$)

What is the $EAN$ of $Zn$ in $[Zn(NH_3)_4]^{2+}$?

What is the value of $n$ in the anionic species $[V(CO)_6]^{n-}$ if it follows the Sidgwick $EAN$ rule and has an octahedral shape?

The effective atomic number of $[A(NH_3)_6]Cl_3$ is $33$. What is the atomic number of element $A$?