Which of the following colloid can be coagulated easily by adding small amount of electrolyte?

Lyophobic colloids

The correct answer is 2. lyophobic colloids.

Lyophobic colloids are colloidal solutions in which the dispersed phase and the dispersion medium are not mutually attracted. This means that the particles of the dispersed phase have a net charge, either positive or negative. When an electrolyte is added to a lyophobic colloid, the ions of the electrolyte can neutralize the charge on the particles of the dispersed phase. This causes the particles to come together and form a precipitate.

Lyophilic colloids, macromolecular colloids, and associated colloids are not easily coagulated by adding small amounts of electrolyte. This is because the particles of these colloids are already attracted to the dispersion medium and do not have a net charge.

Therefore, lyophobic colloids can be coagulated easily by adding small amounts of electrolyte.