Final answer:
Sodium chloride has four Na+ and four Cl- ions per FCC unit cell, cesium chloride contains one Cs+ and one Cl- ion per simple cubic unit cell, and zinc sulfide has four Zn2+ and four S2- ions per FCC unit cell.
Step-by-step explanation:
The formula units per cell for sodium chloride (NaCl), zinc sulfide (ZnS), and cesium chloride (CsCl) refer to the number of complete ion pairs found in their respective crystal lattice unit cells. Sodium chloride crystallizes in a face-centered cubic (FCC) structure, where the unit cell contains four sodium ions and four chloride ions, adhering to the 1:1 stoichiometry of NaCl. In contrast, cesium chloride, with larger cesium ions relative to chloride ions, forms a simple cubic structure. Here, the unit cell consists of one cesium ion and one chloride ion, maintaining the 1:1 stoichiometry indicated by CsCl. Zinc sulfide (zinc blende) also crystallizes in an FCC structure, with four zinc ions and four sulfide ions in each unit cell, resulting in the empirical formula ZnS.