Question

$X$ and $Y$ are two elements which form $X_2{Y}_3$ and $X_3{Y}_4$. If 0.2 mol of $X_2{Y}_3$ weighs 32 g and $0.4$ mole of $X_3{Y}_4$ weighs 92.8 g, the atomic weights of $X$ and $Y$ respectively are :

• A. $16,56$
• B. $16,16$
• C. $56,16$
• D. $56,56$

Answer 1

The correct option is C $56,16$

Weight of 0.2 mol of $X_2{Y}_3=32.0g$.

$\therefore$ Molecular weight $=\frac{32}{0.2}=160g/mol$.

Weight of 0.4 mol of $X_3{Y}_4=92.8g$.

$\therefore$ Molecular weight $=\frac{92.8}{0.4}=232g/mol$.

Now suppose the atomic weight of $X=a$ and atomic weight of $Y=b$

Then $2a+3b=160$ and $3a+4b=232$.

Solving the equations we get, $b=16$ and $a=56$.

Hence (C) is the correct answer.