If the molality of an aqueous solution is $m$ and the mole fraction of the solute is $y$,which of the following relations is correct?

If the mole fraction of the solute in liquid naphthalene $(C_{10}H_{8})$ is $0.2$,then the molality of the solution will be ............ $m$.

$A$ sample of drinking water was found to be severely contaminated with chloroform $(CHCl_{3})$,supposed to be a carcinogen. The level of contamination was $15$ $ppm$ (by mass).
$(i)$ Express this in percent by mass.
$(ii)$ Determine the molality of chloroform in the water sample.

The mole fraction of urea in an aqueous urea solution containing $900 \text{ g}$ of water is $0.05$. If the density of the solution is $1.2 \text{ g cm}^{-3}$,the molarity of the urea solution is . . . . . (Given data: Molar masses of urea and water are $60 \text{ g mol}^{-1}$ and $18 \text{ g mol}^{-1}$,respectively)

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

Which among the following is a unitless physical quantity?