(3) Calculation of ceramic compositions: a) A ruby crystal has a composition (Alo.99Cro.01)2O3. How many Cr3+ ions are there in ruby of dimensions 1 cm3? (Assume that the volume of the unit cell = 0.966ac; lattice parameter a=0.4763 nm, c=1.3009 nm; 6Al2O3 per unit cell) b) Suggest a possible point defect and formula in a synthesized zirconium sulfide (ZrS) if the measured density of Zrs is 4.8 g/cm3. (Assume that ZrS has sodium chloride structure, a=0.514 nm, 4ZrS per unit cell, molar mass Azr=91.22 g/mol, As=32.07 g/mol)