The denticity of an organic ligand, biuret is:

The denticity of a ligand is defined as the number of donor atoms that bind to a single central metal atom in a coordination complex.

Biuret has the molecular formula $$NH_2-CO-NH-CO-NH_2$$. It contains three nitrogen atoms: two terminal amino groups and one central nitrogen atom. These nitrogen atoms have lone pairs that could potentially donate to a metal center.

In coordination chemistry, biuret is most commonly known for forming complexes with metal ions, such as copper(II) in the biuret test. In this test, a violet-colored complex is formed. The structure of this complex involves biuret acting as a bidentate ligand. Specifically, one proton is removed from biuret (deprotonation), and the resulting anion coordinates to the metal ion through two nitrogen atoms: typically, the deprotonated nitrogen (central or terminal) and another nitrogen atom.

For example, in the complex $$[Cu(\text{biuret})_2]^{2+}$$, each biuret ligand binds to the copper ion using two donor atoms, forming a chelate ring. This bidentate coordination is well-established in standard references.

Although biuret has three potential donor atoms, its characteristic denticity in typical complexes is 2, as it uses two donor atoms per ligand to bind to the metal center.

The correct denticity of biuret is 2, corresponding to Option A.