Calculate the mass of iron in $10 \mathrm{kg}$ of iron ore which contains $80\%$ of pure ferric oxide.

If the empirical formula of two compounds is $\mathrm{CH}$ and their vapour densities are $13$ and $39$ respectively, find their molecular formula.

Find the empirical formula of a compound containing $17.64\%$ hydrogen and $82.35\%$ nitrogen.

On analysis, a substance was found to contain:

 $\mathrm{C}=54.54\%, \mathrm{H}=9.09\%, \mathrm{O}=36.36\%$

The vapour density of the substance is $44$, calculate (a) its empirical formula (b) its molecular formula. 

An organic compound, whose vapour density is $45$, has the following percentage composition, 

$\mathrm{H}=2.22\%, \mathrm{O}=71.19\%$ and remaining carbon. Calculate: (a) its empirical formula, (b) its molecular formula.

An organic compound contains $4.07\%$ hydrogen, $71.65\%$ chlorine and remaining carbon. Its molar mass is $98.96$. Find its (a) Empirical formula and (b) Molecular formula.