The donor atoms in ethylene diamine tetra acetate ions are:

The correct answer is Option (2) → Two N and four O atoms

A ligand that binds a metal through more than one donor atom is polydentate. In the ethylenediaminetetraacetate ion (EDTA⁴⁻), two N atoms of the ethylenediamine part each carry a lone pair, and the four –\( \ce{CH2COO^{-}} \) groups each bind through one O atom:

    \( \ce{(^-OOCCH2)2N-CH2-CH2-N(CH2COO^-)2} \)

So EDTA⁴⁻ is a hexadentate ligand with two N and four O donor atoms.

Why the other options are incorrect

• Option (1) Two N and two O atoms — Incorrect. This counts only two of the four carboxylate groups; it would make EDTA tetradentate.

• Option (3) Four N and two O atoms — Incorrect. EDTA has only two nitrogen atoms.

• Option (4) Three N and Three O atoms — Incorrect. EDTA has only two nitrogen atoms, and four carboxylate oxygens bind.

NCERT (2026-27 edition):
Definitions of Some Important Terms Pertaining to Coordination Compounds – “… When a ligand is bound to a metal ion through a single donor atom, as with Cl^–, H₂O or NH₃, the ligand is said to be unidentate. When a ligand can bind through two donor atoms as in H₂NCH₂CH₂NH₂ (ethane-1,2-diamine) or C₂O₄^2– (oxalate), the ligand is said to be didentate and when several donor atoms are present in a single ligand as in N(CH₂CH₂NH₂)₃, the ligand is said to be polydentate. Ethylenediaminetetraacetate ion (EDTA^4–) is an important hexadentate ligand. It can bind through two nitrogen and four oxygen atoms to a central metal ion.”