Question

A substance $A_x{B}_y$ crystallizes in a face - centred cubic lattice in which atoms A 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. Cannot be specified

Answer 1

The correct option is C

$A_{3}B$

$A_x{B}_y\to FCC$, A $\to$ centres of each face
No. of A atoms $=\frac{1}{2}\times 6=3$
B $\to$ all corners
No. of B atoms $=\frac{1}{8}\times 8=1$
Formula $\Rightarrow A_{3}B$