# Question c71f2

May 19, 2017

Let the atomic weight of X be ${A}_{x}$

and the atomic weight of Y be ${A}_{y}$

Given that the percentage of X in the compound =60%

So the percentage of Y in the compound =40%#

The molecular formula of the compound is ${X}_{2} {Y}_{3}$

By dividing the percentage compositions of constituent elements with their respective atomic weights and taking their ratio we get the ratio of number atoms of constituent elements in the compound and this ratio becomes equal $2 : 3$ by the given molecular formula.

So $\frac{60}{A} _ x : \frac{40}{A} _ y = \frac{2}{3}$

$\implies {A}_{y} / {A}_{x} = \frac{2}{3} \times \frac{40}{60} = \frac{4}{9}$

$\implies {A}_{y} = \frac{4}{9} {A}_{x}$

So atomic weight of $Y = \frac{4}{9} \times \text{atomic weight of X}$