In a compound, atoms of elements Y form ccp lattice and those of...

Let atoms of $Y$ in ccp structure $= 100$

Then, number of tetrahedral voids $= 2 \times 100$

$∵$ Number of $X$ atoms $= \dfrac{2}{3}$ rd of tetrahedral voids

$∴$ Number of $X$ atoms $= \dfrac{2}{3} \times 200 = \dfrac{400}{3}$

Hence, formula of compound can be $= {X}_{4}{Y}_{3}$.