The coordination number of the europium ion in the complex [Eu H2O 9]3+ is 9. This is because there are 9 water molecules H2O surrounding and bonded to the europium ion Eu .Europium is a member of the lanthanide series and has an atomic number of 63. Its electronic configuration is [Xe] 4f7 6s2. In the [Eu H2O 9]3+ complex, the europium ion has a +3 charge, which means it loses its 2 electrons from the 6s orbital and 1 electron from the 4f orbital. So, the electronic configuration of Eu3+ is [Xe] 4f6.There are 6 unpaired electrons in the 4f orbital of the europium ion in this complex.To calculate the magnetic moment, we can use the formula: = n n+2 BM Bohr Magneton where n is the number of unpaired electrons. = 6 6+2 BM = 6 8 BM = 48 BMThe magnetic moment of the europium ion in the [Eu H2O 9]3+ complex is approximately 48 Bohr Magnetons.