JEE Main · 2021 · 16 Mar 2021 · Shift 2 · Surface Chemistry

Colloidal particles measure roughly 1 to 1000 nm, while the pores of ordinary filter paper are about a micrometre across, so a sol runs straight through and only an ultrafiltration membrane holds it back. The remaining properties are genuine. By the Hardy-Schulze rule the coagulating power of an ion climbs steeply with its charge, so $\mathrm{A}{\mathrm{l}}^{3+}$ flocculates a negative sol far more effectively than $\mathrm{N}{\mathrm{a}}^{+}$. The dispersed particles are kept in continual zig-zag motion by unbalanced collisions with the molecules of the medium. Being discrete kinetic entities, they also lower the vapour pressure and show the other colligative properties, though feebly because their number concentration is small. The incorrect statement is that ordinary filter paper can stop the flow of colloidal particles.