Question

In a face centred lattice of $X$ and $Y,X$ atoms are present at the corners while $Y$ atoms are at face centres. Then the formula of the compound is

• A. $X{Y}_3$
• B. $XY$
• C. $X_{3}Y$
• D. $X_2{Y}_3$

Answer 1

The correct option is A $X{Y}_3$


In $FCC$ each atom in the face is shared between two cubes, while each atom at the corner is shared among eight cubes.
Number of $X$ in each cube $=\frac{1}{8}\times 8=1$
Number of $Y$ in each cube $=6\times \frac{1}{2}=3$
So $X$ and $Y$ are in the ratio of $1:3$ and the formula is $X{Y}_3$.