Diethylene triamine (DETA) is a versatile compound that serves as a chelating agent, a polydentate ligand, and a tridentate ligand. Let's break down these three aspects:

Chelating Agent:
Chelating agents are compounds that have the ability to form multiple bonds with a metal ion, thereby creating a stable complex. Diethylene triamine can form chelate complexes with metal ions by donating its lone pairs of electrons to the metal ion, effectively surrounding and "holding" the metal ion in a coordination complex.

Polydentate Ligand:
A polydentate ligand is a molecule that can donate multiple lone pairs of electrons to a central metal ion. Diethylene triamine has three amine groups, each of which can act as a donor atom to bind to a metal ion. This makes DETA a polydentate ligand, forming multiple coordination bonds with the metal ion.

Tridentate Ligand:
A tridentate ligand is a specific type of polydentate ligand that can form three coordination bonds with a metal ion. In the case of diethylene triamine, all three amine groups can bind to a metal ion, making it a tridentate ligand.
Therefore, Diethylene triamine exhibits all these characteristics - acting as a chelating agent, a polydentate ligand, and a tridentate ligand. Its ability to form stable coordination complexes with metal ions makes it a valuable compound in various chemical and industrial applications.