Which of the following statements about colloids is false?

First, recall that a colloidal dispersion contains particles whose diameters lie between $$1\,\text{nm}$$ and $$1000\,\text{nm}$$. Such particles bear an electric charge and remain dispersed because the like-charges on different particles repel each other. Now we examine each statement one by one and relate it to the well-known facts of colloid chemistry.

Statement A: “When silver nitrate solution is added to potassium iodide solution, a negatively charged colloidal solution is formed.”
When $$AgNO_{3}$$ is added to an excess of $$KI$$, the reaction $$Ag^{+ + I^{-} \to AgI \ (s)}$$ produces finely divided $$AgI$$, which gets dispersed as a colloid. Because there is excess $$I^{-}$$ in the medium, these iodide ions are adsorbed on the freshly precipitated $$AgI$$ particles, giving each particle an overall negative charge. The phenomenon is called ionic adsorption. Therefore Statement A is correct.

Statement B: “Freezing point of colloidal solution is lower than true solution at same concentration of a solute.”
For any solution we use the colligative formula  $$\Delta T_f = iK_f m,$$ where $$\Delta T_f$$ is the depression in freezing point, $$K_f$$ is the cryoscopic constant of the solvent, $$m$$ is the molality, and $$i$$ is the van’t Hoff factor that counts the effective number of solute particles in the solution.

In an ordinary (true) solution the solute exists as individual molecules or ions, so $$i$$ equals the actual number of particles produced per formula unit (for nonelectrolytes $$i \approx 1$$, for electrolytes $$i > 1$$). In a colloidal solution, however, each dispersed entity is an aggregate containing many molecules; the entire aggregate behaves as a single particle. Consequently the number of particles per kilogram of solvent is drastically smaller, so the value of $$i$$ (and effectively $$m \times i$$) is smaller for the colloid.

Because $$\Delta T_f$$ is directly proportional to $$iK_f m$$, the depression in freezing point for the colloid is smaller, meaning its actual freezing point is higher than that of the true solution at the same overall concentration. Hence the wording “lower than true solution” is wrong. Statement B is therefore false.

Statement C: “Colloidal particles can pass through ordinary filter paper.”
The pore size of common filter paper is of the order of micrometres, much larger than the size of colloidal particles (nanometres). Therefore colloidal particles indeed pass through ordinary filter paper, though they are retained by special membranes such as parchment or cellophane. Statement C is correct.

Statement D: “When excess of electrolyte is added to colloidal solution, colloidal particle will be precipitated.”
Adding a large concentration of an electrolyte introduces counter-ions that neutralise the surface charge on the colloidal particles. Once the charge is neutralised, the electrostatic repulsion vanishes and the particles aggregate, leading to coagulation or precipitation. This is known as electrolyte-induced coagulation. Statement D is correct.

We find that the only statement which does not agree with the established theory is Statement B.

Hence, the correct answer is Option B.