See image — AITS & Test Series Chemistry Question

💡 Solution & Explanation

Number of atoms of X in FCC packing (at corners and face centres of cubic unit cell) = 1 1 8 6 4 8 2     Number of atoms of Y at octahedral voids = 4 Along one body diagonal there are two X atoms and one Y-atom. No. of effective atoms of X after removal 1 15 4 2 8 4     No. of atoms of Y after removal = 4 – 1 = 3 15 x : y : 3 4  = 5 : 4 Simplest formula = X5Y4 a = 5, b = 4, a/b = 1.25