Question

What is the formula of a compound in which the element $Y$ forms ccp lattice and atoms of $X$ occupy $\frac{1}{3}rd$ of tetrahedral?

• A. $X{Y}_3$
• B. $X_2{Y}_3$
• C. $X_{2}Y$
• D. $XY$

Answer 1

The correct option is B $X_2{Y}_3$

Number of tetrahedral voids formed $=2\times$ number of elements $Y$

Number of atoms of element $Y$ in the ccp unit cell =4

Number of tetrahedral voids formed $=2\times 4=8$

Number of tetrahedral voids occupied by atoms of $X$ $=\frac{1}{3}\times 8$

Ratio of the number of atoms of $X$ and $Y$ $=\frac{8}{3}:4=2:3$

Hence, the formula of compound is $X_2{Y}_3$