The coordination number of Gd3+ ion in GdCl3 is 6. In GdCl3, the Gd3+ ion is surrounded by six chloride ions Cl- in an octahedral arrangement.When Gd3+ forms a complex with the EDTA ligand, its coordination environment changes significantly. EDTA ethylenediaminetetraacetic acid is a hexadentate ligand, meaning it can bind to a central metal ion through six donor atoms. In the case of Gd3+, the EDTA ligand binds to the Gd3+ ion through its two nitrogen atoms and four oxygen atoms from the carboxylate groups, forming a 1:1 complex.As a result, the coordination number of Gd3+ remains 6 in the Gd-EDTA complex, but its coordination environment changes from being surrounded by six chloride ions to being surrounded by the six donor atoms of the EDTA ligand. This leads to a more stable and highly soluble complex in aqueous solutions.