Calculate the molecular formula of compound which contains 20% Ca and 80% Br (by wt.) if molecular weight of compound is 200. (Atomic wt. Ca= 40, Br= 80)

$\begin{array}{|ccccc|}\hline \text{ Elements }& \%& \%/\text{ Atomic mass }& \text{ Simple ratio }& \text{ Simplest whole no. }\\ \mathrm{Ca}& 20& 20/40=0.5& 1& 1\\ \mathrm{Br}& 80& 80/80=1& 2& 2\\ \hline\end{array}$Hence : Empirical formula $= {\mathrm{CaBr}}_2$

$\mathrm{n}=\frac{200}{200}=1$

$\begin{array}{r}\frac{20}{100}\times \frac{200}{40}=n_{\mathrm{Ca}}\\ \frac{80}{100}\times \frac{200}{80}=n_{\mathrm{Br}}\end{array}$