Question

In a compound, atoms of element $Y$ form ccp lattice and those of element $X$ occupy $2/3rd$ of tetrahedral voids. How many atoms of $X$ are present in one formula unit of the compound?

Answer 1

Answer: 4

No. of $Y$ atoms per unit cell in ccp lattice $=4$
No. of tetrahedral voids $=2\times 4=8$
No. of tetrahedral voids occupied by $X$
$=\frac{2}{3}\times 8=\frac{16}{3}$
Therefore, formula of the compound
$=X_{16/3}{Y}_4$
$=X_{16}{Y}_{12}$
$=X_4{Y}_3$