Adding sodium chloride (NaCl) to a ferric oxide sol (Fe₂O₃) will cause flocculation, meaning the particles in the sol will clump together and settle out of solution.

Here's why:

* Ferric oxide sols are stabilized by electrostatic repulsion: The iron oxide particles in the sol carry a positive charge, repelling each other and preventing them from clumping. This is due to the presence of ions like OH⁻ adsorbed on the surface of the particles.

* NaCl disrupts the electrostatic repulsion: When you add NaCl, the sodium ions (Na⁺) and chloride ions (Cl⁻) from the salt compete with the existing ions in the sol. This disrupts the electrical double layer surrounding the iron oxide particles, reducing the electrostatic repulsion.

* Flocculation occurs: With reduced repulsion, the particles can now come close enough to each other to experience attractive forces (like van der Waals forces) and clump together, forming larger aggregates. These aggregates are too heavy to remain suspended and will settle out of the solution as a precipitate.

In summary:

Adding NaCl to a ferric oxide sol disrupts the electrostatic stabilization of the particles, leading to flocculation and sedimentation. This process is an example of coagulation, where particles are brought together to form larger aggregates.