Highest osmotic pressure is shown by a solution of

Concentrations of ions in $0.1 \mathrm{M}$ aluminium sulphate $\left[\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\right]$ is $$ \begin{aligned} &=0.1\left[2 \times\left(\mathrm{Al}^{3+}\right) \text { ions }+3 \times\left(\mathrm{SO}_{4}^{2-}\right) \text { ions }\right] \\ &=0.1[2 \times 1+3 \times 1]=0.1 \times 5=0.5 \mathrm{M} \end{aligned} $$ Concentrations of ions in $0.1 \mathrm{M}$ potassium nitrate (KCl) is $=0.1\left(1\right.$ mole of $\mathrm{K}^{+}+1$ mole of $\left.\mathrm{Cl}^{-}\right)$ $$ =0.1 \times 2=0.2 \mathrm{M} $$ Concentration of ions in $0.1 \mathrm{M}$ magnesium chloride $\left(\mathrm{MgCl}_{2}\right)$ is $=0.1\left(1\right.$ mole of $\mathrm{Mg}^{2+}+2$ moles of $\left.\mathrm{Cl}^{-}\right)$ $$ =0.1 \times 3=0.3 \mathrm{M} $$ Concentration of ions in $0.1 \mathrm{M}$ barium chloride $\left(\mathrm{BaCl}_{2}\right)$ is $=0.1\left(1\right.$ mole of $\mathrm{Ba}^{2+}+2$ moles of $\left.\mathrm{Cl}^{-}\right)$ $$ =0.1 \times 3=0.3 \mathrm{M} $$ $\therefore$ Order of concentration is $0.1 \mathrm{M} \mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}>0.1 \mathrm{M} \mathrm{KCl}>0.1 \mathrm{MgCl}_{2}$ $=0.1 \mathrm{M} \mathrm{BaCl}_{2}$ $\because$ Osmotic pressure is colligative property and, it depends on concentration of ions. $\therefore$ Order of osmotic pressure is $$ \begin{aligned} 0.1 \mathrm{M}\left(\mathrm{Al}_{2} \mathrm{SO}_{4}\right)_{3}>0.1 \mathrm{M} \mathrm{KCl} &>0.1 \mathrm{M} \mathrm{MgCl}_{2} \\ &>0.1 \mathrm{M} \mathrm{BaCl}_{2} \end{aligned} $$