Correct Statements Regarding Properties of Colloidal Systems

To determine the correct statement(s) regarding colloidal systems, let us analyze each option individually:

1. Analysis of Option (A):

   • Peptization is defined as the process of converting a freshly prepared precipitate into a colloidal sol by shaking it with a dispersion medium in the presence of a small amount of an electrolyte (known as a peptizing agent).
   • On the other hand, the process of settling down or precipitating colloidal particles by adding an electrolyte is termed coagulation or flocculation.
   • Thus, statement (A) is incorrect.

2. Analysis of Option (B):

   • Depression in freezing point ($\Delta T_f$) is a colligative property and depends on the number of dissolved particles per unit volume: $\Delta T_f = i \cdot K_f \cdot m \propto \text{number of particles per unit volume}$
   • For the same mass concentration, colloidal particles consist of large aggregates of molecules or ions. Thus, the total number of independent solute particles in a colloidal sol is significantly smaller than that in a true solution of the same concentration.
   • As a result, the depression in freezing point is smaller for a colloidal solution than for a true solution: $(\Delta T_f)_{\text{colloid}} < (\Delta T_f)_{\text{true solution}}$
   • Since the freezing temperature of the solution is given by $T_f = T_f^\circ - \Delta T_f$ (where $T_f^\circ$ is the freezing point of the pure solvent), a smaller depression ($\Delta T_f$) results in a higher freezing point: $T_{f,\text{colloid}} > T_{f,\text{true solution}}$
   • Thus, statement (B) is correct.

3. Analysis of Option (C):

   • Surfactants behave as normal strong electrolytes at low concentrations. However, above a threshold concentration known as the Critical Micelle Concentration (CMC) and above a specific temperature known as the Krafft temperature ($T_k$), surfactant molecules aggregate to form micelles.
   • The CMC depends on temperature because micellization is driven by hydrophobic interactions and hydration changes of the hydrophilic head groups, both of which are temperature-dependent thermodynamic phenomena.
   • Thus, statement (C) is correct.

4. Analysis of Option (D):

   • Colloids are classified based on the nature of the dispersed phase particles into:
     1. Multimolecular colloids (e.g., Gold sol, $S_8$ sol)
     2. Macromolecular colloids (e.g., Starch, cellulose, proteins, polymers)
     3. Associated colloids (Micelles, e.g., Soaps and synthetic detergents)
   • Micelles belong to the category of associated colloids, not macromolecular colloids.
   • Thus, statement (D) is incorrect.

Correct Answer: The correct statements are B and C.