The Oxidation State and Effective Atomic Number (EAN) of Cobalt in ${[Co{F_6}]^{ - 2}}$are respectivelyA.3 and 36B.4 and 35C.4 and 37D.2 and 35

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Hint:The atomic number of Cobalt is 27 and ${F^ - }$is a monodentate ligand.
Formula used:
${\text{EAN = Z - x + 2nL}}$
Oxidation state of ${\text{Co = (overall charge of) - (no}}{\text{. of\;ions )(Oxidation state of)}}$

Effective Atomic Number or EAN is a number which represents the total number of electrons that are present and are surrounding the nucleus of the metal atom in the given metal complex. It is composed of the metal atom’s electrons and the bonding electrons from the surrounding electron-donating atoms and molecules.
Mathematically, the Effective Atomic Number can be calculated by using the following formula:
${\text{EAN = Z - x + 2nL}}$
Where,
Z= Atomic number of the metal in the complex
x = Oxidation state of the metal in the complex
n= Number of the ligands
L = Number of coordinate bonds formed by ligand
For monodentate ligands, L =1

For the given metal complex ${[Co{F_6}]^{ - 2}}$;
Calculating the oxidation state:
In order to calculate the oxidation state of a metal in a metal complex, you subtract the oxidation numbers of the ligands from the overall charge of the compound.
Now, the oxidation state of ${F^ - }$ is -1
Hence the oxidation state of Cobalt in the given metal complex is:
Oxidation state of Co = (overall charge of ${[Co{F_6}]^{ - 2}}$) – (no. of ${F^ - }$ ions )(Oxidation state of ${F^ - }$)
Oxidation state of Co = (-2) - (6)(-1)
Oxidation state of Co = -2 + 6
Oxidation state of Co = +4
Calculating the EAN:
 $\begin{array}{*{20}{l}} {{\text{EAN = Z - x + 2nL}}} \\ {{\text{EAN = 27 - 4 + 2}}\left( {\text{6}} \right)\left( {\text{1}} \right)} \\ {{\text{EAN = 27 - 4 + 12}}} \\ {{\text{EAN = 35}}} \end{array}$

Hence, Option B is the correct.