Question

in the complex ion, $ {[Fe(EDTA)]^ - } $ the coordination number and oxidation state of central metal ion is:
 $ a.{\text{ }}C.N. = 6,O.N. = + 3 \\
  b.{\text{ }}C.N. = 1,O.N. = - 1 \\
  c.{\text{ }}C.N. = 4,O.N. = + 2 \\
  d.{\text{ }}C.N. = 3,O.N. = \_2 \\ $

Answer 1

Hint :Ligands: The donor atoms, molecules or anions which donate a pair of electrons to the metal atom/ion are called ligands. Hence ligands are Lewis bases. Coordination number- It may be defined as the number of Coordinate bonds formed with central atoms/ion by the ligands. For example, in the coordination entity $ {[Ag{(CN)_2}]^ - } $ the coordination number of Ag is 2.

Complete Step By Step Answer:
Coordination number of central atoms is determined only by the number of sigma bonds formed by ligands with central metal ions. Pi bonds if formed are not counted for this purpose.
Oxidation number-The central metal ion or atom, in a complex is the charge present on it if all the ligands are removed along with the electron pairs that are shared with the central atom. It is represented by Roman numerals in parentheses after the name of the central atom. For example, the oxidation number of Co in $ {[Co{(N{H_3})_6}]^{3 + }} $ , us written as $ Co(III) $ .
In the complex $ {[Fe(EDTA)]^ - } $ , the central metal atom is Fe. The denticity of EDTA which is Polydentate, is 6. So coordination number= 6
The charge on EDTA : -4
Oxidation state of Fe :
 $ x + ( - 4) = - 1 \\
  x = + 3 \\ $
So coordination number is =6, oxidation number is +3.

Note :
In a coordination entity, the atom/ion to which a fixed number of ions)/group is attached in a definite geometrical arrangement around it, is called Central atom/ion. For example $ {K_2}[Pt{(Cl)_6}],P{t^{ + 4}} $ is a central metal ion. Central metal ion or atom accepts lone pairs l of electrons from the ligands hence it acts as Lewis acid.