What is the value of percent atom economy when an organic compound of formula weight $75 \ u$ is obtained from reactants having sum formula weight $225 \ u$?

The $NaNO_3$ weighed out to make $50 \ mL$ of an aqueous solution containing $70.0 \ mg$ $Na^{+}$ per $mL$ is $...... \ g$.
(Rounded off to the nearest integer) [Given : Atomic weight in $g \ mol^{-1}$ - $Na : 23$; $N : 14$; $O : 16$]

How many grams of $HCl$ are required to prepare $1500 \, mL$ of $0.1 \, N \, HCl$ aqueous solution?

What volume of $0.1 \, M \, HCl$ in $cm^3$ is required to react completely with $1 \, g$ of pure calcium carbonate $(CaCO_3)$?

The amount of $KMnO_4$ required to prepare $100 \ mL$ of $0.1 \ N$ solution in alkaline medium is ............... $g$.

$KMnO_4$ reacts with oxalic acid according to the equation,$2MnO_4^- + 5C_2O_4^{2-} + 16H^{+} \to 2Mn^{2+} + 10CO_2 + 8H_2O$. Here,$20 \ mL$ of $0.1 \ M$ $KMnO_4$ is equivalent to: