Question

An alloy of two metals A and B has cubic close packing structure, where atoms of B occupy lattice points and atoms of A occupies 25% of the tetrahedral voids. The composition of the alloy is

• A. $AB$
• B. $A{B}_2$
• C. $A_2{B}_3$
• D. $A{B}_4$

Answer 1

The correct option is B

$A{B}_2$

Lattice points of ccp lattice are 8 corners and 6 face centres.

Number of atoms of $B=8\times \frac{1}{8}+6\times \frac{1}{2}=4$

Total number of tetrahedral voids = 8

Number of atoms of A = $8\times \frac{1}{4}=2$

So each unit cell of alloy has one atom of A and two atoms of B.

The composition of Alloy is $A{B}_2$