An ionic compound has a unit cell consisting of A ions at the corners of a cube and B ions on the centres of the faces of the cube.

(c) : Number of A ions per unit cell =1/8 x 8 = 1
Number of B ions per unit cell =1/2 x 6 = 3
Empirical formula = AB₃.

Correct option (b) AB₃

Explanation:

Unit cell consists of A ions at the corners.

Thus, the number of ions of the type A =8/8=1

Unit cell consists of g ions at the center of the six faces.

Thus, the number of ions of type B =6/2=3

[Each corner is shared by B cubes and each face is shared by 2 faces]

Thus, the formula is AB₃.

Correct option: (D) AB₃

Explanation:

A as corners of cube; 1/8 x 8 = 1.

B as faces of cube; 1/2 x 6 = 3

A : B = 1 : 3 

∴ The empirical formula for this compound would be AB₃