How many $cc$ of water should be added to $200 \ cc$ of $seminormal$ $NaOH$ solution to make it $decinormal$?

$25.3 \ g$ of sodium carbonate,$Na_2CO_3$ is dissolved in enough water to make $250 \ mL$ of solution. If sodium carbonate dissociates completely,the molar concentration of sodium ions,$Na^{+}$,and carbonate ions,$CO_3^{2-}$,are respectively:
(Molar mass of $Na_2CO_3 = 106 \ g \ mol^{-1}$)

The molality of $90\%$ ${H_2SO_4}$ solution is [density $= 1.8 \ g/mL$].

$A$ solution contains $7.8 \ g$ of benzene $(C_6H_6)$ and $46.0 \ g$ of toluene $(C_6H_5CH_3)$. What is the mole fraction of benzene?

$2 \ g$ of substance $A$ is added to $18 \ g$ of water to form a solution. Calculate the mass percentage of the solute. (in $\%$)

The volume of $10 \ N$ and $4 \ N$ $HCl$ required to make $1 \ L$ of $7 \ N$ $HCl$ are