Question

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. The empirical formula for this compound would be

(a) AB 

(b) A₂B

(c) AB₃ 

(d) A₃B

Answer 1

(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.