Question

A compound of formula $A_2{B}_3$ has the hcp lattice. Which atom forms the hcp lattice and what fraction of tetrahedral voids is occupied by the other atoms :

• A. hcp lattice-A, $\frac{2}{3}$ Tetrachedral voids-B
• B. hcp lattice-B, $\frac{1}{3}$ Tetrachedral voids-A
• C. hcp lattice-B, $\frac{2}{3}$ Tetrachedral voids-A
• D. hcp lattice-A, $\frac{1}{3}$ Tetrachedral voids-B

Answer 1

Answer: (B)

$A_2{B}_3$ has HCP lattice
If $A$ form HCP, then $\frac{3^{th}}{4}$ of THV must occupied by B to form $A_2{B}_3$ .
If $B$ form HCP, then $\frac{1^{th}}{3}$ of THV must occupied by A to form $A_2{B}_3$