CsCl: crystallizes in a cubic structure that has a Cs+ at each corner and a Cl- at the center of the unit cell. If the ions radii of Cs+ and Cl- ions are 1.69 A° and 1.81 A°. respectively; Predict the lattice constant (a) and compare with the value of (a) calculated from the observed density of CsCl, 3.97 gm/cm3.