For what ratio of volumes should $0.4 \, M \ HCl$ and $0.9 \, M \ HCl$ be mixed to obtain a solution of $0.7 \, M \ HCl$?

What volume of $0.8 \ M$ solution contains $0.1 \ mole$ of the solute? (in $mL$)

When $5 \, mL$ of $N \, HCl$,$20 \, mL$ of $N/2 \, H_2SO_4$,and $30 \, mL$ of $N/3 \, HNO_3$ are mixed together and the volume is made up to $1 \, L$,the normality of the resulting solution is:

$1.5 \ mol$ of $O_2$ combine with $Mg$ to form oxide $MgO$. The mass of $Mg$ (atomic mass $24$) that has combined is ............. $g$.

$A$ 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:

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