If $50 \ mL$ of $0.5 \ M$ oxalic acid is required to neutralize $25 \ mL$ of $NaOH$ solution, the amount of $NaOH$ in $50 \ mL$ of the given $NaOH$ solution is . . . . . . $g$.

Define stoichiometry and stoichiometric calculation.

In the reaction,$2Al_{(s)} + 6HCl_{(aq)} \rightarrow 2Al^{3+}_{(aq)} + 6Cl^{-}_{(aq)} + 3H_{2(g)}$

The number of chlorine atoms in $20 \, mL$ of chlorine gas at $STP$ is ..... $\times 10^{21}$. (Round off to the Nearest Integer).
[Assume chlorine is an ideal gas at $STP$,$R = 0.083 \, L \, bar \, mol^{-1} \, K^{-1}$,$N_{A} = 6.023 \times 10^{23}$]

$A$ solution of $CaCl_2$ is $0.5 \, mol/L$. The number of moles of chloride ions in $500 \, mL$ of this solution will be:

$20.0 \ g$ of a magnesium carbonate sample decomposes on heating to give carbon dioxide and $8.0 \ g$ magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample? $(At. \ wt. \ of \ Mg = 24)$