Pick out the complex compound in which the central metal atom obeys the $EAN$ rule strictly.

The Effective Atomic Number $(EAN)$ of iron in potassium ferricyanide is .......

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

The atomic number of cobalt is $27$. The $EAN$ of cobalt in $Na_{3}[Co(NO_{2})_{4} Cl_{2}]$ 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 one of the following does not follow Sidgwick $EAN$ rule?