Question

Atoms of element $B$ form hcp lattice and those of the element $A$ occupy $2/3^{rd}$ of tetrahedral voids. What is the formula of the compound formed by the elements $A$ and $B$?

• A. $A_2{B}_3$
• B. $A{B}_3$
• C. $A_3{B}_4$
• D. $A_4{B}_3$

Answer 1

The correct option is D $A_4{B}_3$

The number of tetrahedral voids formed is equal to twice the number of atoms of element $B$ and only $2/3^{rd}$ of these are occupied by the atoms of element $A$. Hence, the ratio of the number of atoms of $A$ and $B$ is $2\times \left(2/3\right):1$.
$\Rightarrow 4:3$ and the formula of the compound is $A_4{B}_3$.