What will be the volume of $O_2$ gas at $STP$ which is obtained by thermal decomposition of $30.62 \ g$ $KClO_3$,with $80\%$ purity?

For the reaction $4FeCr_2O_4 + 8Na_2CO_3 + 7O_2 \rightarrow 8Na_2CrO_4 + 2Fe_2O_3 + 8CO_2$,what is the stoichiometric ratio of the reactants $(FeCr_2O_4 : Na_2CO_3 : O_2)$?

How many grams of $Cu(NO_3)_2$ are needed to obtain $1 \ g$ of copper? $($ Atomic mass: $Cu = 63.5, N = 14, O = 16$ $)$

How many grams of $CaCO_3$ must be decomposed to produce $20 \ L$ of $CO_2$ at $750 \ torr$ and $27 \ ^\circ C$?

$40\%$ 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?

The ratio of amounts of $H_2S$ needed to precipitate all the metal ions from $100 \ mL$ of $1 \ M$ $AgNO_3$ and $100 \ mL$ of $1 \ M$ $CuSO_4$ will be