Answer 1

Bidentate ligands: The ligands which bind to central metal through two donor atoms are called bidentate ligands.

e.g.

1. Ethylenediammine binds to the central metal atom through two nitrogen atoms.

2. Similarly, Oxalate ligand   `"C"_2"O"_4^{2-}` utilizes electron pair on each of its negatively charged oxygen atoms on linking with central metal.