Which of the following is correct for lyophilic sol: (a) Irreversible sol (b) Formed from inorganic substances (c) Readily coagulated by addition of electrolyte (d) Self stabilized

Lyophilic sols, sometimes referred to as reversible sols, showcase a remarkable ability to undergo a reversible process. This means that these sols can be dehydrated to remove the dispersion medium, often a solvent, and later reconstituted by simply reintroducing the solvent.

The key driving force behind this reversibility lies in the strong interaction between the dispersed phase (usually made up of large organic molecules) and the dispersion medium (typically water or another solvent). When the solvent is removed, the remaining compound often retains a structure that can easily reabsorb the solvent.

This property of lyophilic sols is in stark contrast to lyophobic sols, which do not readily reabsorb a solvent once it's been removed due to weaker interactions between the dispersed phase and the dispersion medium. Hence, lyophilic sols are frequently utilized in industries that require processes such as freeze-drying, where reversibility is fundamental.

A colloidal system, or colloidal dispersion, is a two-phase system comprising a dispersed phase (particles) and a continuous phase (dispersion medium), where the size of the dispersed particles is in the range of 1 to 1000 nanometers.

Colloidal systems are unique because their particle size allows them to possess properties distinct from those of fine suspensions or true solutions. The particles in a colloid are small enough to remain dispersed and not settle out under the influence of gravity. However, they are large enough to scatter light, a phenomenon known as the Tyndall effect, which makes colloids appear 'cloudy' or 'milky' when light passes through them.

Lyophilic sols are a subtype of colloidal solutions where the dispersed phase has a strong affinity towards the dispersion medium. These sols are often more stable, and they illustrate how interaction at the molecular level influences the macroscopic properties of the system, including viscosity and interfacial tension.

The stability of colloids is a measure of how well a colloidal system maintains its homogeneity, preventing the dispersed particles from aggregating or settling over time. The stability is greatly influenced by the nature of the interaction between the dispersion medium and the dispersed particles.

Lyophilic sols exhibit exceptional stability due to the natural affinity between the dispersed phase and the solvent. This is why they don’t coagulate or precipitate out easily upon the addition of an electrolyte. On the other hand, lyophobic sols are less stable and can be destabilized by various factors, including pH changes, the addition of salts, or a shift in temperature.

Various factors contribute to the stabilization of colloids, including:

• Electric double layer: Each particle in a colloid is often surrounded by a layer of ions that prevents close approach of particles, providing electrostatic stabilization.
• Solvent layering: Especially in lyophilic colloids, where the solvent forms a structured layer around the particles, enhancing stability through steric hindrance.
• Surfactants: These compounds can adsorb onto particles within lyophobic colloids and can provide stability via both electrostatic and steric mechanisms.

Understanding these factors is crucial for the practical manipulation and application of colloids in various industrial and research settings.