Copper bonds with six electron pairs on EDTA to form the complex shown below where the central metal species is copper(II):
EDTA4− usually binds to a metal cation through its two amines and four carboxylates. Many of the resulting coordination compounds adopt octahedral geometry. Many complexes of EDTA4− adopt more complex structures due to either the formation of an additional bond to water, i.e. seven-coordinate complexes, or the displacement of one carboxylate arm by water. The Fe(III) complex of EDTA is seven-coordinate.
The scenario that in the presence of an excess EDTA, metals can bind to more than one EDTA molecules does not exist. The problem stems from the fact that the complex is weakened upon incorporating another molecule of EDTA. The optimal strength of the complex is when EDTA and the metal adopt octahedral geometry.
The unusual property of EDTA is its ability to chelate or complex metal ions in 1:1 metal-to-EDTA complexes.
answer (c) the ratio of moles of metal and edta is 1:1