What is the actual volume occupied by water molecules present in $20 \ cm^3$ of water (in $cm^3$)?

In a $20\%$ aqueous solution of $H_2O_2$,the mole fraction of water is $.......$.

Natural gas is a mixture of methane and ethane. The heat produced by the complete combustion of $10 \, L$ of this mixture at $S.T.P.$ is $476.6 \, kJ$. Given $\Delta H_{comb} (CH_4) = -894 \, kJ \, mol^{-1}$ and $\Delta H_{comb} (C_2H_6) = -1500 \, kJ \, mol^{-1}$,calculate the percentage of methane and ethane in the mixture by volume.

How is concentrated $H_2SO_4$ diluted?

The density of an equimolar mixture of $CH_4$ and $CO$ at $STP$ is ............... $g \, L^{-1}$.

$10 \ g$ $NaHCO_{3(s)}$ sample is heated in open to constant weight,the residue is titrated against $0.1 \ M \ HCl$ in presence of phenolphthalein as an indicator,$500 \ mL$ of acid was required to reach end point hence $PERCENT$ purity of sample is $............... \%$.