In the balanced equation of the following reaction, the ratio of $a / b$ is: $aCaCO_3 + bH_3PO_4 \rightarrow pCa_3(PO_4)_2 + qCO_2 + rH_2O$

$3O_2 + 2N_2 \to 2N_2O_3$
$9 \ mol$ of $O_2$ and $14 \ mol$ of $N_2$ are allowed to react. When $3 \ mol$ of $O_2$ remains unreacted,how many moles of $N_2O_3$ would have been produced?

$0.4 \text{ g}$ of dihydrogen is made to react with $7.4 \text{ g}$ of dichlorine to form hydrogen chloride. The volume of hydrogen chloride formed at $273 \text{ K}$ and $1 \text{ bar}$ pressure is: (in $\text{ L}$)

When $12 \ L$ of $H_2$ and $11.2 \ L$ of $Cl_2$ are mixed and allowed to react according to the equation $H_{2(g)} + Cl_{2(g)} \rightarrow 2HCl_{(g)}$,what is the final composition of the mixture?

In a closed vessel at $STP$,$50 \, L$ of $CH_4$ is ignited with $750 \, L$ of air (containing $20 \% \ O_2$). The number of moles of $O_2$ remaining in the vessel on cooling to room temperature is closest to

In the Haber process,$30 \ L$ of dihydrogen and $30 \ L$ of dinitrogen were taken for the reaction,which yielded only $50\%$ of the expected product. What will be the composition of the gaseous mixture under the aforesaid condition in the end?