Final answer:
One EDTA molecule can bind to two magnesium ions.
Step-by-step explanation:
The ligand EDTA is a hexadentate ligand, meaning it can form six coordinate bonds with a metal ion. Each coordinate bond involves the donation of one lone pair of electrons from the EDTA molecule to the metal ion. Since magnesium has a charge of 2+, it can form two coordinate bonds with one EDTA molecule. Therefore, one EDTA molecule can bind to two magnesium ions.