How many grams of $BaCO_3$ are produced when excess $CO_2$ is passed through $0.205 \ mol$ of $Ba(OH)_2$?

The volume of oxygen required for complete combustion of $0.25 \ mol$ of methane at $S.T.P.$ is (in $dm^{3}$)

Gastric juice contains about $3.0 \ g$ of $HCl$ per liter. If a person produces about $2.6 \ liters$ of gastric juice per day,find the number of antacid tablets required to neutralize all the $HCl$ produced. Consider each antacid tablet contains $400 \ mg$ of $Al(OH)_3$. [Given,atomic masses: $Al=27, O=16, H=1, Cl=35.5$]

Element $A$ reacts with oxygen to form a compound $A_2O_3$. If $0.359 \ g$ of $A$ reacts to form $0.559 \ g$ of the compound,the atomic mass of $A$ is:

Equal volumes of $0.1 \ M$ $AgNO_3$ and $0.2 \ M$ $NaCl$ are mixed. The concentration of $NO_3^-$ ion in the mixture will be ............ $M$.

At $STP$,the volume of $4.4 \, g$ of an unknown gas is $2.24 \, L$. Which of the following is this gas?