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Q.
In a compound, atoms of element $Y$ form $c c p$ lattice and those of element $X$ occupy $2 / 3^{\text {rd }}$ of tetrahedral voids. The formula of the compound will be
The Solid State
Solution:
Number of $Y$ atoms per unit cell in ccp lattice $(N)=4$
Number of tetrahedral voids $=2 N=2 \times 4=8$
Number of tetrahedral voids occupied by $X$ $=2 / 3^{\text {rd }}$ of the tetrahedral void $=2 / 3 \times 8=16 / 3$
Hence, the formula of the compound will be, $X_{16 / 3} Y_{4}=X_{4} Y_{3}$