Question

Two compound $p$ (at $w75)$ and $q\left(atmwght16\right)$ combine to give a compound having $75.8$% of $p$, then the formula will be:

• A. $X_4{Y}_3$
• B. $X_2{Y}_5$
• C. $X_5{Y}_3$
• D. $X_2{Y}_3$

Answer 1

The correct option is D $X_2{Y}_3$

Let the formula be $X_a{Y}_b$

%$x=\frac{a\times \text{atomic weight of}X}{\text{Molecular weight}}\times 100$

Similarly, % $Y=\frac{b\times \text{atomic weight of}Y}{\text{Molecular weight}}\times 100$

$\therefore 75.8=\frac{a\times 75}{\text{Molecular weight}}\times 100$

$\therefore 24.2=\frac{b\times 16}{\text{Molecular weight}}\times 100$

$\therefore \frac{a}{b}\times \frac{75}{16}=\frac{75.8}{24.2}$

$\Rightarrow \frac{a}{b}\approx \frac{2}{3}\Rightarrow$ Compound is $X_2{Y}_3$ .