The coordination number of the [Nd H2O 8]3+ complex ion is 8, which means that there are eight water molecules H2O surrounding the neodymium Nd ion in the complex. The coordination geometry of this complex ion is a square antiprism. In this geometry, the Nd ion is at the center, and the eight water molecules are arranged with four above and four below the central ion, forming two square planes that are slightly twisted with respect to each other.The stability of the [Nd H2O 8]3+ complex ion in aqueous solutions is influenced by several factors:1. Charge of the central ion: The Nd ion has a charge of +3, which creates a strong electrostatic attraction between the positively charged Nd ion and the negatively charged oxygen atoms of the water molecules. This strong attraction contributes to the stability of the complex ion.2. Size of the central ion: The Nd ion has a relatively large ionic radius, which allows it to accommodate eight water molecules in its coordination sphere. The larger the central ion, the more ligands it can accommodate, and the more stable the complex ion will be.3. Nature of the ligand: Water is a neutral ligand, which means that it does not have a charge. This makes it less likely to compete with other negatively charged ligands for binding to the Nd ion, contributing to the stability of the complex ion in aqueous solutions.4. Chelate effect: Although the chelate effect is not directly applicable to the [Nd H2O 8]3+ complex ion since water is a monodentate ligand, it is still worth mentioning. The chelate effect states that complexes with multidentate ligands ligands that can bind to the central ion through multiple sites are generally more stable than complexes with monodentate ligands. If the [Nd H2O 8]3+ complex ion were to encounter a multidentate ligand in solution, it could potentially form a more stable complex, leading to the displacement of the water molecules.Overall, the stability of the [Nd H2O 8]3+ complex ion in aqueous solutions is influenced by the charge and size of the central Nd ion, the nature of the water ligands, and the potential presence of competing multidentate ligands.