Question

A substance $A_x{B}_y$ crystallizes in an f.c.c. lattice in which atoms of $‘A^{\prime }$ occupy each corner of the cube and atoms of $‘B^{\prime }$ occupy the centres of each face of the cube. Identify the correct composition of the substance $A_x{B}_y$.

• A. $A{B}_3$
• B. $A_4{B}_3$
• C. $A_{3}B$
• D. None of the above

Answer 1

The correct option is C $A_{3}B$

Number of A atoms $=\frac{1}{2}\times 6=3$

Number of B atoms $=\frac{1}{8}\times 8=1$ (corners)

Therefore, the formula is $A_{3}B$.