• # question_answer  A compound formed by elements X and Y crystallises in a cubic structure in which the X atoms are at the corners of a cube and the Y atoms are at the face centres. The formula of the compound is A)  $X{{Y}_{3}}$                                    B)  ${{X}_{3}}Y$ C)  $XY$                                   D)  $X{{Y}_{2}}$

As atoms X are  present at the eight corners of the cube, therefore, number of atoms of X in the unit cell $=\frac{1}{8}\times 8=1$ As atoms Y are present at the face centres of the 6 faces of the cube, therefore, number of atoms of V in the unit cell  $=\frac{1}{2}\times 6=3$ Hence, the formula of compound is $X{{Y}_{3}}$