The vapour pressure of water at room temperature is lowered by $5\%$ by dissolving a solute in it, then the approximately molality of solution is :

The vapour pressure of water at room temperature is lowered by $5\%$ by dissolving a solute in it, then the approximate molality of solution is $3$.

$\frac{0.05P^{\circ }}{P^{\circ }}=m\times \frac{18}{1000}$

$m=2.8~3$

Hence, option D is correct.