If $100 \ g$ of a $0.2 \ m$ aqueous solution is diluted by adding $200 \ g$ of water, what will be the molality of the resulting solution?

If one mole of a substance is present in $1 \ kg$ of solvent,then

$10.30 \; mg$ of $O_2$ is dissolved in $1 \; L$ of seawater with a density of $1.03 \; g/mL$. The concentration of $O_2$ in $ppm$ is:

$25.3 \ g$ 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 $Na_2CO_3 = 106 \ g \ mol^{-1}$)

What will be the molality of $10\%$ w/w aqueous solution of $NaOH$ (in $m$)? (Molecular mass of $NaOH = 40 \ g \ mol^{-1}$)

$A$ solution of two components containing $n_{1}$ moles of the $1^{st}$ component and $n_{2}$ moles of the $2^{nd}$ component is prepared. $M_{1}$ and $M_{2}$ are the molecular weights of component $1$ and $2$ respectively. If $d$ is the density of the solution in $g \ mL^{-1}$, $C_{2}$ is the molarity and $x_{2}$ is the mole fraction of the $2^{nd}$ component, then $C_{2}$ can be expressed as