Which of the following can function as a chelating agent? and why?
a. nh3
b. co2
c. oh-
d. c2o4 2-

In oxalate,  you need have to have two donor atoms to make a chelate ligand which barely means, NH3 and OH^- is ruled out. You have to consider the structure of Carbon dioxide (CO2) and deduce why both O atoms cannot coordinate to the same M^n+ ion. 

18