How many grams of $CaCO_3$ must be decomposed to produce $20 \ L$ of $CO_2$ at $750 \ torr$ and $27 \ ^\circ C$?

How many grams of a dibasic acid (molar mass = $200 \ g/mol$) are present in $100 \ mL$ of its $0.1 \ N$ aqueous solution (in $g$)?

What volume of $O_{2(g)}$ measured at standard condition will be formed by the action of $100 \ mL$ of $0.5 \ N \ KMnO_4$ on hydrogen peroxide in an acidic solution? The skeleton equation for the reaction is:
$KMnO_4 + H_2SO_4 + H_2O_2 \to KHSO_4 + MnSO_4 + O_2 + H_2O$
(Answer in $L$)

For the complete combustion of $15 \ mL$ of a gaseous hydrocarbon at $300 \ K$ and $1 \ atm$ pressure,$375 \ mL$ of air containing $20\% \ O_2$ by volume is required. After combustion,the gases occupy $330 \ mL$. Assuming that the water formed is in liquid state and the volumes are measured at the same temperature and pressure,find the formula of the hydrocarbon.

Which of the following is the correct formula to determine percent atom economy?

How many moles of $H_2O_2$ are required for the decolorization of $1$ mole of $KMnO_4$?