Question

What will be the simplest formula of the comopund if in a crystalline solid, atoms of X form fcc packing and the atoms of Y occupy all the octahedral voids?

• A. $XY$
• B. $X{Y}_2$
• C. $X_{4}Y$
• D. $X{Y}_4$

Answer 1

The correct option is A $XY$

In fcc packing (at corners and face centres of cubic unit cell) $\text{Number of atoms of X}=8\times \frac{1}{8}+6\times \frac{1}{2}=4$
No of octahedral voids = Number of atoms in FCC = 4
$\text{Number of atoms of Y}=4$
Formula:
$X_4{Y}_4$
Simplest formula:
$XY$