Question

Suppose the elements X and Y combine to form two compounds $X{Y}_2$ and $X_3{Y}_2$. When 0.1 mole of $X{Y}_2$ weighs 10 g and 0.05 mole of $X_3{Y}_2$ weighs 9 g, the atomic weights of X and Y are

• A. 20, 30
• B. 30, 20
• C. 40, 30
• D. 60, 40

Answer 1

The correct option is C 40, 30

Let atomic weight of $X$ is $A_X$ and Y is $A_Y$

$n_{X{Y}_2}=0.1=\frac{10}{A_X+2A_Y}$

$A_X+2A_Y=100\dots \dots \left(1\right)$

$n_{X_3{Y}_2}=0.05=\frac{9}{3A_X+2A_Y}$

$3A_X+2A_Y=180\dots \dots \left(2\right)$

On solving eq. (1) and (2)

$A_X=40,A_Y=30$