• # question_answer A solution containing two non-interacting solid solutes A and B in the mass ratio 1:1 is isotonic with another solution 1 and 2 (in the same volume of the solution) having mass ratio 3 : 5. Calculate the molar mass ratio of A and B. A)  $\frac{1}{2}$                                    B)  $\frac{1}{3}$ C)  $\frac{3}{5}$                                    D)  $\frac{2}{3}$

Assume that the total masses of solutes in the two solutions 1 and 2 are 3 m and 5 m respectively. Then, if ${{M}_{1}}$ and ${{M}_{2}}$ are the molar masses, the total number of moles in a given volume of solution 1 at T K is $\frac{1.5m}{{{M}_{1}}}+\frac{1.5m}{{{M}_{2}}}$ In solutions 2, this number is $\frac{0.5m}{{{M}_{1}}}+\frac{4.5m}{{{M}_{2}}}$ The solutions are isotonic $\therefore$ $\frac{1.5m}{{{M}_{1}}}+\frac{1.5m}{{{M}_{2}}}=\frac{0.5m}{{{M}_{1}}}+\frac{4.5m}{{{M}_{2}}}$ By calculation, $\frac{1}{{{M}_{1}}}=\frac{3}{{{M}_{2}}}$ $\therefore$    $\left( \frac{{{M}_{1}}}{{{M}_{2}}} \right)=\frac{1}{3}$