Q6: In ionic crystals, anions of the relatively larger size and densely arranged so as to avoid their direct contact, whereas cations of relatively smaller size occupy the positions equivalent to the vacant space produced by anions. For this reason, if the radii of cation and anion are described by rc and ra, respectively, some correlations are recognized between the coordination numbers and the size radio of rv/ra. Estimate the specific values of rv/ra for cases that cations are surround by anions with the coordination numbers of 3,4,6 and 8 . Fig. A Four typical geometries for arraying equal spheres