Question

In a F.C.C lattice, atom A occupies the corner positions and atom B occupies the face centre positions. If one atom of B is missing from one of the face centred points, the formula of the compound is

• A. $A{B}_2$
• B. $A_2{B}_3$
• C. $A_2{B}_5$
• D. $A_{2}B$

Answer 1

The correct option is C $A_2{B}_5$

Effective No. of A atoms $=\frac{1}{8}\times 8=1$
Effective No. of B atoms $=\frac{1}{2}\times 8$
One is missing $=\frac{5}{2}$
Therefore formula is $A_1{B}_{\frac{5}{2}}=A_2{B}_5$