What is the percentage atom economy during the conversion of reactant to product if the formula weight of reactants is $246 \ u$ and that of the product is $123 \ u$ (in $\%$)?

$40\%$ of a mixture of $0.2 \ mol$ of $N_2$ and $0.6 \ mol$ of $H_2$ reacts to give $NH_3$ according to the equation:
$N_{2(g)} + 3H_{2(g)} \rightleftharpoons 2NH_{3(g)}$
at constant temperature and pressure. What is the ratio of the final volume to the initial volume of gases?

For the combustion reaction $C_2H_{6(g)} + nO_{2(g)} \to CO_{2(g)} + H_2O_{(l)}$,what is the ratio of the stoichiometric coefficients of $CO_2$ and $H_2O$ in the balanced equation?

$15 \ mL$ of $N/10$ $NaOH$ solution completely neutralizes $12 \ mL$ of $H_2SO_4$ solution. The normality of $H_2SO_4$ solution will be:

Concentrated $HCl$ is $10 \, N$. How much volume of concentrated $HCl$ is required to prepare $1000 \, mL$ of $1 \, N$ $HCl$ by dilution?

The weight of calcium oxide formed by burning $20 \ g$ of calcium in excess oxygen is $.... \ g$