When excess $CO_2$ is passed through a solution containing $0.205 \ mol$ of $BaCO_3$,what is the mass of $Ba(HCO_3)_2$ formed in grams?

The concentration of a $100 \ mL$ solution containing $X \ g$ of $Na_2CO_3$ (molecular weight $= 106$) is $Y \ M$. The values of $X$ and $Y$ are respectively.

The mass of a mixture containing $NaCl$ and $NaBr$ is $4.0 \ g$. If $Na$ is $30 \%$ of the total mixture,the composition of $NaCl$ in the mixture is (in $\%$)

Volume of air needed for complete combustion of $10 \ L$ of $C_2H_4$ is :
$($Assume air contains $20\%$ of $O_2$ by volume$)$ (in $L$)

The formula of a metallic oxide is $MO$. What will be the formula of its phosphate?

Concentrated sulfuric acid is $95\%$ by weight and its density is $1.8 \ g \ cm^{-3}$. What volume of concentrated acid in $cm^3$ is required to prepare $4 \ L$ of $0.4 \ M \ H_2SO_4$ solution (in $.7$)?