${\mathrm{FeCl}}_3$on reaction with ${\mathrm{K}}_4 \left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$ in aq. solution gives blue color. These are separated by a semipermeable membrane PQ as shown. Due to osmosis, there is

SPM allows only solvent molecules to pass through it. These are separated by a semipermeable membrane PQ as shown. Due to osmosis, there is no blue color formation.