What will be the mass percentage of an aqueous solution of $NaOH$ in which the mole fraction of $NaOH$ is $0.2$ (in $\% W/W$)?

Which of the following methods of expressing concentration does not change with temperature?

If $80 \ g$ of copper sulphate $CuSO_{4} \cdot 5H_{2}O$ is dissolved in deionised water to make $5 \ L$ of solution. The concentration of the copper sulphate solution is $x \times 10^{-3} \ mol \ L^{-1}$. The value of $x$ is .... .
[Atomic masses: $Cu = 63.54 \ u, S = 32 \ u, O = 16 \ u, H = 1 \ u$]

The molality of $15\% \,(w/V)$ solution of $H_2SO_4$ with density $1.1\, g/cm^3$ is

$1 \ g$ of a solute is added to $18 \ g$ of water. In this aqueous solution,what is the mass per cent of the solute (in $\%$)?

Molarity is expressed as