A solid is composed of two elements, X and Y. Atoms of X are arranged in an FCC lattice. Atoms of Y — Solid State Chemistry Question

💡 Solution & Explanation

Since X forms the FCC lattice, effective number of X atoms ($Z$) = $4$. In an FCC lattice, there are 4 octahedral voids and 8 tetrahedral voids. Y occupies all 4 octahedral voids and half of the tetrahedral voids ($8 \times \frac{1}{2} = 4$). Total Y atoms = $4 + 4 = 8$. The ratio X : Y is 4 : 8, making the empirical formula $XY_2$.