Which of the following fcc structure contains cations in alternate tetrahedral voids ?

In Zinc Blende (ZnS) structure, -2 S are in CCP sites and +2 Zn are in alternate tetrahedral voids. Other examples of Zinc Blende structure are CuBr, CuCl, CuI, AgI, BeS. Hence the correct answer is option (b) 111. The ionic radii of Na⁺, K⁺ and Br– are 137, 148 and 195 pm, respectively. The coordinaiton number of cation in KBr and NaBr structures are, respectively, (a) 8, 6 (b) 6, 4 (c) 6, 8 (d) 4, 6 Limiting radius Ratio / x r r 0.414 0.7326 6 0.732 0.9998 8 x CN x CN For KBr, / 148 /195 0.76 x r r For NaBr, / 137 /195 0.702 x r r SOLID STA