What is the percent atom economy if the formula weight of reactants and the formula weight of products are $45 \ u$ and $35 \ u$ respectively (in $\%$)?

When oxygen is heated in the presence of a catalyst,$15 \%$ of it is converted into ozone. How many grams of oxygen are required to produce $33.6 \, L$ of $O_3$ at $STP$?

$A$ sample of $CaCO_3$ and $MgCO_3$ weighing $2.21 \ g$ is ignited to a constant weight of $1.152 \ g$. The composition of the mixture is:
(Given molar mass in $g \ mol^{-1}: CaCO_3 = 100, MgCO_3 = 84$)

The weight of $1 \ L$ of a hydrocarbon is more than that of $1 \ L$ of $CO_2$ at the same temperature and pressure. What is the molecular formula of the hydrocarbon?

$100 \, mL$ of a mixture of $NaOH$ and $Na_2SO_4$ is neutralized by $10 \, mL$ of $0.5 \, M$ $H_2SO_4$. Hence,the mass of $NaOH$ in $100 \, mL$ solution is ........... $g$.

What is the weight of oxygen required for the complete combustion of $2.8 \, kg$ of ethylene? (in $kg$)