Ethylene diaminetetraacetate (EDTA) ion is :

The correct answer is: Hexadentate ligand with four “O” and two “N” donor atoms.

Step-by-step Explanation:

1. Concept of Denticity:
Denticity refers to the number of donor atoms that a single ligand uses to bind to a central metal atom or ion in a coordination complex. Based on the number of donor atoms, ligands are classified as monodentate (one donor atom), bidentate (two donor atoms), tridentate (three donor atoms), and so on.

2. Structure of EDTA^4-:
Ethylenediaminetetraacetate (EDTA^4-) is a coordinate ligand synthesized by replacing the hydrogen atoms of ethylenediamine with four acetate groups. The structure of the EDTA^4- ion is represented as:

$({\mathrm{OOC}}^{-}-{\mathrm{CH}}_2{)}_{2}N-{\mathrm{CH}}_2-{\mathrm{CH}}_2-N({\mathrm{CH}}_2-{\mathrm{COO}}^{-}{)}_2$

3. Identifying the Donor Atoms:
Within a single EDTA^4- ion, there are two types of atoms that have lone pairs of electrons available to coordinate with a central metal ion:

• Two Nitrogen (N) atoms: Each of the two amine nitrogen atoms contains one lone pair of electrons.
• Four Oxygen (O) atoms: Each of the four carboxylate groups (-COO^-) contains a negatively charged oxygen atom that acts as an electron donor.

4. Conclusion:
Because EDTA^4- possesses a total of six donor atoms (two nitrogen atoms and four oxygen atoms) that can bind simultaneously to a metal ion, it functions as a hexadentate ligand.