What is the weight (in $g$) of $Na_2CO_3$ (molar mass $= 106$) present in $250 \ mL$ of its $0.2 \ M$ solution?

Define stoichiometry and stoichiometric calculation.

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 $\%$)?

$1 \ mol$ of metal '$M$' reacts completely with alcohol to give $1.5 \ mol$ of $H_2$. What is the valency of metal '$M$'?

At the same temperature and pressure,if the mass of $3 \ L$ of a hydrocarbon is equal to the mass of $3 \ L$ of $CO_2$,what is the molecular formula of the hydrocarbon?

Under the same conditions of temperature and pressure,the ratio of the masses of equal volumes of $O_2$,$O_3$,and $SO_2$ will be respectively .............