A given sample of chalk contains $55\%$ by mass of calcium carbonate. Calculate the percentage of calcium, carbon, and oxygen in the sample.

A compound on analysis gave the following percentage composition.
$\mathrm{Na}-14.31\%, \mathrm{S}-9.97\%, \mathrm{H}-6.22 \%, \mathrm{O}-69.5\%$. The molecular mass of the substance is $322$. Find its molecular formula assuming that all the hydrogen atoms are present in combination with oxygen as water of crystallisation. (At. mass $\mathrm{Na}=23, \mathrm{H}=1, \mathrm{S}=32, \mathrm{O}=16$)

An organic compound contains $52.18\%$ carbon and $13.04\%$ hydrogen, the remaining being oxygen. The vapour density of the compound is $23$. Calculate the molecular formula.

A compound with molecular weight $108$, contained $88.89\%$ $\mathrm{C}$ and $11.11\% \mathrm{H}$. Calculate its molecular formula.

Avogadro number has value $6.023\times {10}^{23}$.

Equal volumes of all gases contain equal number of molecules at all temperature and pressure.