The simplest formula of a compound containing 50% of element X(atomic mass = 10) and 50%.ofthe element Y(atomic mass = 20) by weight is:

Let mass of compound $= 100 gm$

Then mass of $X = 50 gm$

Then mass of $Y = 50 gm$

Mole of $\mathrm{X}=\frac{50}{10}=5$

Mole of $Y=\frac{50}{10}=5$

Molecular formula  $={\mathrm{X}}_5{\mathrm{Y}}_{25}={\mathrm{X}}_2\mathrm{Y}$

$\begin{array}{l}\frac{50}{10}:\frac{50}{20}\\ 2 : 1\\ X_2 Y\end{array}$