What is the weight (in $g$) of $Na_2CO_3$ (molar mass $= 106$) present in $250 \ mL$ of its $0.2 \ M$ solution?

What will be the volume of $CO_2$ at $NTP$ obtained on heating $10 \ g$ of ($90\%$ pure) limestone (in $L$)?

The mass of nitrogen that combines with $40 \ g$ of oxygen in $N_2O_5$ is ............ $g$.

What is the normality of a $1 \, M$ solution of $H_3PO_4$?

$A$ person consumes $640 \, g$ of $O_2$ daily. If all the $O_2$ is used for the conversion of sugar into $CO_2$ and $H_2O$,how much sucrose $(C_{12}H_{22}O_{11})$ is consumed in the body per day and how much heat in $kJ$ is produced (in $.33$)? Given: $\Delta H_{combustion} \text{ of sucrose} = -5645 \, kJ \, mol^{-1}$.

Given the ratio of masses of nitrogen and oxygen in a particular gaseous mixture is $4: 1$. Calculate the ratio of the number of their molecules.