An aqueous solution of a non-volatile solute is such that the vapour pressure is 25% lesser than that of water at same temperature. The molality of the solution will be :

An aqueous solution of a non-volatile solute is such that the vapour pressure is 25% lesser than that of water at same temperature. The molality of the solution will be :

$\begin{array}{l}\frac{P_A^{\circ }-P_S}{P_A}=\frac{n_B}{w_A}\times 1000\times \frac{M_A}{1000}\\ \frac{25}{75}=m\times \frac{18}{1000}\\ m=\frac{1000}{54}\end{array}$