Coordination compounds
The coordination compounds are very important in biological systems (like human, plant and animal's body), metallurgy, analytical chemistry, medicine etc. Chlorophyll, Hemoglobin, vitamin B12 etc. are coordination compounds of various metals. They are also called complex compounds and formed by two main entities, metal and ligands. Some ligands are Poly-dentate, like EDTA, which is used in the estimation of hardness of water with Ca2+ and Mg2+ ions. Gold and silver make [Au(CN)2]− and [Ag(CN)2]− type complex ions in aqueous solution during extraction of metals. In photography, developing film form a complex ion [Ag (S2O3)2]3−. A complex compound of platinum (Pt), cis-platin is used in the treatment of cancer. Some metals can be refined by making their complex compounds, like impure Nickel is converted to [Ni(CO)4] complex. All these coordination compounds may be colored or colorless, paramagnetic or diamagnetic, low spin or high spin, and arranged in particular geometry and hybridization. Isomerism is shown by these complexes due to different arrangement of ligands around the central metal atom.
ligand (EDTA)4- is........
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Hexadentate ligand
The denticity of a ligand is the number of donor atoms through which it binds to the central metal ion: one for a unidentate ligand such as \( \ce{NH3} \), two for a didentate (bidentate) ligand such as ethane-1,2-diamine. An ambidentate ligand, such as \( \ce{NO2^-} \), can bind through either of two different donor atoms, but through only one at a time. For EDTA4− (ethylenediaminetetraacetate):
\( \displaystyle \text{Denticity}=2\ (\text{N})+4\ (\text{O})=6 \)
So EDTA is a hexadentate ligand.
NCERT (2026-27 edition):
Definitions of Some Important Terms Pertaining to Coordination Compounds – …
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| 21-05 S2 18-05 S2 12-05 S2 | – | – | – | – |