Mass of magnesium required to produce $220 \ mL$ of hydrogen gas at $STP$ on reaction with excess of dil. $HCl$ is (Given: Molar mass of $Mg$ is $24 \ g \ mol^{-1}$)

The number of millimoles and milliequivalents of $Ba(OH)_2$ in $0.2 \, L$ of $0.2 \, M \, Ba(OH)_2$ solution are respectively:

Concentrated nitric acid used in laboratory work is $68 \%$ nitric acid by mass in aqueous solution. What should be the molarity of such a sample of the acid if the density of the solution is $1.504 \, g \, mL^{-1}$ (in $, M$)?

How many kilograms of $CaCO_3$ must be heated to obtain $56$ kilograms of $CaO$? [Atomic masses: $Ca = 40, C = 12, O = 16$]

$4.0 \,g$ of $NaOH$ are contained in one decilitre of solution. Its molarity would be ......... $M$.

Aqueous $HCl$ reacts with $MnO_{2(s)}$ to form $MnCl_{2(aq)}$, $Cl_{2(g)}$ and $H_{2}O_{(l)}$. What is the weight (in $g$) of $Cl_{2}$ liberated when $8.7 \ g$ of $MnO_{2(s)}$ is reacted with excess aqueous $HCl$ solution? (Given Molar mass in $g \ mol^{-1}$: $Mn=55$, $Cl=35.5$, $O=16$, $H=1$)