A compound formed by elements X and Y crystallizes in the cubic structure where Y atoms are at the corners of the cube and X atoms are at the alteranate faces. What is the formula of the compound?

In the given compound; there must be 8 corners in a cube,

So, as the Y atoms are at corners, so each of the Y atom will contribute 1/8 part towards a particular unit cell.

The no. of Y atoms per unit cell = 8 x 1/8 = 1

Further, the X atoms are at the alternate faces so they will be available only at one of the opposite faces, so the contribution of each of  the X-atoms will be 1/2 towards the face center.

The no. of X-atoms = 2 x 1/2 = 1

Hence, the formula of the compound will be "XY" and the compound will be represented as;