ETHYLENEDIAMINETETRAACETATE (EDTA) is a famous polydentate ligand. It is

1. EDTA has six potential donor atoms: 2 nitrogen atoms and 4 oxygen atoms (from the four carboxylate groups). 2. When fully deprotonated and bound, all six donor atoms can coordinate to a single metal centre. 3. So EDTA is HEXADENTATE — capable of forming six metal-donor bonds. 4. This is why EDTA forms exceptionally STABLE complexes with metal ions (chelate effect compounded six times) — used in water-hardness titrations, as an anticoagulant, and for heavy-metal detoxification. 5. With a hexadentate ligand and an octahedral metal, ONE EDTA molecule completely occupies the coordination sphere. 6. Other options misidentify the ligand type. _Source: syllabus Chemistry Part 1, Ch 5, §5.2 (Polydentate ligands — EDTA example) + Table 5.1, p. 3._