Question

A compound formed by elements $X$ and $Y$ crystallizes in a cubic structure in which the $X$ atoms are at the comers of a cube and the $Y$ atoms are at the face - centres. The formula of the compound is

• A. $ X{{Y}_{3}} $
• B. $ {{X}_{3}}Y $
• C. $ XY $
• D. $ X{{Y}_{\,}}_{2} $

Answer 1

Answer: (A)

In unit cell, X-atoms at the comers
$ =\frac{1}{8}\times 8=1 $
Y-atoms at the face centres
$ =\frac{1}{2}\times 6=3 $
Ratio of X and $ Y=1:3 $ .
Hence, formula is $ X{{Y}_{3}} $ .