Which of the following aqueous solutions has osmotic pressure nearest to that of an equimolar solution of ${\mathrm{K}}_4\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$

We know that the value of colligative property is directly proportional to number of particles of solute. 

Since ${\mathrm{K}}_4\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$ and ${\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3$ both form 5 ions on dissociation. Hence osmotic pressure of ${\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3$ solution will be nearest to that of equimolar solution of ${\mathrm{K}}_4\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$