Which of the following is always a bidentate ligand?

Ammonia (NH_3$), water (H_2O$), and carbon monoxide (CO$) are monodentate ligands because they donate only one pair of electrons to the central metal atom or ion.<br><br>Ethylenediamine (H_2N-CH_2-CH_2-NH_2$) is a bidentate ligand because it has two nitrogen atoms, each with a lone pair of electrons, which can simultaneously coordinate to the central metal atom or ion.

Answer: Ethylenediamine