The correct answer is Option (1): CN is an ambidentate ligand
Option 1: $CN^-$ is an ambidentate ligand (Correct)
- Fact: A cyanide ion ($CN^-$) can link to a central metal atom through either the Carbon atom (cyano) or the Nitrogen atom (isocyano).
- Definition: Ligands that have two different donor atoms and can coordinate through either one are called ambidentate ligands.
Option 2: $EDTA^{4-}$ is a tetradentate ligand (Incorrect)
- Fact: Ethylenediaminetetraacetate ($EDTA^{4-}$) is actually a hexadentate ligand.
- Mechanism: It binds through two Nitrogen atoms and four Oxygen atoms (from the four acetate groups), making it very effective for chelation.
Option 3: $CH_3NH_2$ is a bidentate ligand (Incorrect)
- Fact: Methylamine ($CH_3NH_2$) is a monodentate ligand.
- Mechanism: It only has one lone pair on the Nitrogen atom available for coordination. It lacks a second donor atom to be bidentate.
Option 4: $C_2O_4^{2-}$ is not a Chelating ligand (Incorrect)
- Fact: The oxalate ion ($C_2O_4^{2-}$) is a bidentate ligand that coordinates through two Oxygen atoms.
- Definition: Because it coordinates via two donor atoms to a single metal ion, it forms a 5-membered ring structure. This ring-forming property makes it a chelating ligand.
- Hence, statement is incorrect.
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