Question

Two elements $X$ and $Y$ (atomic mass of $X=75\text{u}$,$Y=16\text{u}$) combine to give a compound that has 76% of $X$. The formula of the compound is:

• A. $XY$
• B. $X_{2}Y$
• C. $X_2{Y}_2$
• D. $X_2{Y}_3$

Answer 1

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

Calculation of the empirical formula of the compound:
$\begin{array}{cccccc}\text{Element}& \text{\% in compound}& \text{Atomic mass}& \text{No. of moles}& \text{Simple ratio}& \text{Simple whole number}\\ X& 76& 75& \frac{76}{75}=1.01& \frac{1.01}{1.01}=1& 1\times 2=2\\ Y& 24& 16& \frac{24}{16}=1.51& \frac{1.51}{1.01}=1.5& 1.5\times 2=3\end{array}$
So, the empirical formula will be $X_2{Y}_3$