The stability of inorganic compounds can be determined by comparing their lattice energies. Lattice energy is the energy required to separate one mole of a solid ionic compound into its gaseous ions. The higher the lattice energy, the more stable the compound. Lattice energy is directly proportional to the product of the charges of the ions and inversely proportional to the sum of their ionic radii.In the case of CaF2, MgF2, and BaF2, all three compounds have the same type of ions F- and a divalent metal cation and the same crystal structure fluorite structure . Therefore, the main factor affecting their stability is the size of the metal cation.The ionic radii of the metal cations are as follows:- Mg2+ 0.72 is smaller than Ca2+ 1.00 , which is smaller than Ba2+ 1.35 .Since lattice energy is inversely proportional to the sum of the ionic radii, the compound with the smallest metal cation will have the highest lattice energy and thus be the most stable. Therefore, the stability order of these compounds is:MgF2 > CaF2 > BaF2MgF2 has the highest lattice energy due to the smaller size of the Mg2+ ion, which results in stronger electrostatic interactions between the ions in the crystal lattice. CaF2 has intermediate stability, and BaF2 has the lowest stability due to the larger size of the Ba2+ ion, which results in weaker electrostatic interactions between the ions in the crystal lattice.