How many grams of ethanol must be added to $1.0 \ kg$ of water to have a mole fraction of ethanol equal to $0.2$?

The molality of a solution is defined as:

What is the molarity of the solution formed by adding $3 \, L$ of $0.5 \, M$ $NaOH$ solution to $2.5 \, L$ of $1 \, M$ $NaOH$ solution?

Which unit of concentration value does not change with change in temperature?

If the mole fraction of a solute in liquid naphthalene $(C_{10}H_8)$ is $0.2$,then the molality of the solution will be .............. $m$.

Sea water,which can be considered as a $6 \ M$ solution of $NaCl$,has a density of $2 \ g \ mL^{-1}$. The concentration of dissolved oxygen $(O_2)$ in sea water is $5.8 \ ppm$. Then the concentration of dissolved oxygen $(O_2)$ in sea water is $x \times 10^{-4} \ m$. $x = ............$ $(Nearest \ integer)$
Given: Molar mass of $NaCl$ is $58.5 \ g \ mol^{-1}$. Molar mass of $O_2$ is $32 \ g \ mol^{-1}$.