The minimum number of moles of $O_2$ required for complete combustion of $1$ mole of propane and $2$ moles of butane is...

$20 \ mL$ of $CO_2$ gas are passed over excess of red hot coke. The volume of $CO$ evolved is ............. $mL$.
$CO_{2(g)} + C_{(s)} \to 2CO_{(g)}$

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

$19 \ g$ of a mixture containing $NaHCO_3$ and $Na_2CO_3$ on complete heating liberated $1.12 \ L$ of $CO_2$ at $STP$. The weight of the remaining solid was $15.9 \ g$. What is the weight (in $g$) of $Na_2CO_3$ in the mixture before heating?

If $1$ mole of $N_2$ occupies a volume of $22.4 \, L$ at $NTP$,what is the density of $N_2$ in $g/L$?

What is the volume occupied by $2.5 \ mol$ of ammonia gas at $\text{STP}$ (in $dm^3$)?