How many $g$ of a dibasic acid (Mol. wt. $= 200$) should be present in $100 \ mL$ of its aqueous solution to give decinormal strength?

$A$ pre-weighed vessel is filled with $O_2$ and weighed at $STP$. It is then evacuated and filled with $SO_2$ gas at the same temperature and pressure,and weighed again. The weight of $O_2$ will be:

The mass of $BaCO_3$ produced when excess $CO_2$ is bubbled through a solution of $0.205 \ mol$ $Ba(OH)_2$ is ............ $g$.

Amount of oxygen required for combustion of $1 \, kg$ of a mixture of butane and isobutane is ............. $kg$.

Calculate the mass in $kg$ of $4.48 \ dm^3$ of carbon dioxide $(CO_2)$ at $STP$.

$100 \, mL$ of $Na_{3}PO_{4}$ solution contains $3.45 \, g$ of sodium. The molarity of the solution is $..... \times 10^{-2} \, mol \, L^{-1}$ $(Nearest \, integer)$.
[$Atomic \, Masses - Na: 23.0 \, u, O: 16.0 \, u, P: 31.0 \, u$]