Multiple choice What is the coordination number of [Cr(C2O4)3]3-? 1 2 4 6 Reveal answer Fill a bubble to check yourself D Correct answer Explanation The oxalate ion (C2O4)2- is a bidentate ligand, coordinating through two oxygen atoms. In [Cr(C2O4)3]3-, three oxalate ligands each donate two electron pairs, giving 3×2=6 donor atoms bonded to chromium, so CN=6.