Question

In a face-centred cubic arrangement of A and B atoms, the atoms of element A are at the corners of the unit cell, and atoms of element B are at the face centres. One of the A atoms is missing from one corner in the unit cell. The simplest formula of the compound is :

• A. $A_7{B}_3$
• B. $A{B}_3$
• C. $A_7{B}_{24}$
• D. $A_8{B}_{21}$

Answer 1

The correct option is C $A_7{B}_{24}$

Number of atoms of A from corners of unit cell= $\frac{7}{8}$

Number of atoms of B from faces of unit cell=3

Thus $A:B=\frac{7}{8}:3=7:24$

Formula is $A_7{B}_{24}$