Chemistry - Solid State Question with Solution | TestHub

Let the number of atoms of element Y in the hcp lattice be $N$.

The number of octahedral voids in a close-packed structure is equal to the number of atoms in the lattice, which is $N$.

Since atoms of element X occupy $\frac{1}{3}$ of the octahedral voids, the number of atoms of X is $\frac{N}{3}$.

The ratio of the number of atoms of X to that of Y is $\frac{N}{3}:N=1:3$.

Therefore, the formula of the compound is ${\text{XY}}_3$.

Answer: ${\text{XY}}_3$