Which of the following is a correct statement?

We need to identify the correct statement about colloidal solutions. Option A, “Brownian motion destabilises sols,” is incorrect because Brownian motion actually stabilises sols by preventing the colloidal particles from settling down under gravity; the continuous random motion keeps the particles suspended. Option B, “Any amount of dispersed phase can be added to emulsion without destabilising it,” is incorrect because adding too much dispersed phase can cause phase inversion or destabilisation since emulsions have a limited capacity to hold dispersed phase. Option C, “Mixing two oppositely charged sols in equal amount neutralises charges and stabilises colloids,” is incorrect as mixing oppositely charged sols causes mutual coagulation (precipitation), not stabilisation; the opposite charges neutralise each other, removing the electrostatic stabilisation, and the particles aggregate and settle.

Option D, “Presence of equal and similar charges on colloidal particles provides stability to the colloidal solution,” is correct because when all colloidal particles carry the same type of charge (either all positive or all negative), they repel each other. This electrostatic repulsion prevents the particles from coming together and coagulating, thus providing stability to the colloidal solution. This is known as electrostatic stabilisation.

The correct answer is Option D.