Ethylene diaminetetraacetate (EDTA) ion is :

Ethylene‑diaminetetraacetate (EDTA) is a poly‑anion that can bind a metal ion through several donor atoms attached to its skeleton.

1. Identify the functional groups in EDTA.
– The molecule contains an ethylene‑diamino backbone: –CH₂–CH₂– with two nitrogen atoms (‑NH‑) at each end.
– Each nitrogen is attached to two acetate (‑CH₂COO⁻) groups, giving four carboxylate groups in total.

2. Count the potential donor atoms.
– Each nitrogen atom in the –NH‑ groups possesses a lone pair that can coordinate to a metal ion. This provides **2 nitrogen donor sites**.
– Each carboxylate group has two oxygen atoms, but only one of the oxygens typically coordinates to a metal (the other remains non‑bonding). With **four** carboxylate groups, this yields **4 oxygen donor sites**.

3. Determine the total denticity.
Adding the donor sites together: 2 (N) + 4 (O) = **6 donor atoms**. A ligand that uses six donor atoms to bind a metal is called **hexadentate**.

4. Summarize the ligand classification.
Therefore, the EDTA ion acts as a **hexadentate ligand** that donates **four oxygen atoms** from its carboxylate groups and **two nitrogen atoms** from its ethylenediamine backbone.