Which of the following is not an example of lyophilic colloids?

Silver solution

The correct answer is option 4. Silver solution.

Lyophilic colloids are colloidal systems where the dispersed phase has a strong affinity for the dispersion medium. Let's evaluate each option:

1. Starch solution: Starch is hydrophilic and has a strong affinity for water, making it a lyophilic colloid. Starch molecules readily form colloidal solutions with water.

2. Gelatin: Gelatin is derived from collagen, and it forms stable colloidal solutions in water due to its strong affinity for water molecules. Therefore, gelatin is a lyophilic colloid.

3. Gum: Gums, such as gum arabic or xanthan gum, are also hydrophilic colloids that form stable colloidal solutions in water. They have a strong affinity for water, making them lyophilic colloids.

4. Silver solution: Silver particles in a solution do not have a strong affinity for the dispersion medium (usually water). Instead, silver particles are typically stabilized in colloidal form by adsorbed ions or molecules on their surfaces. Silver solutions are often prepared by reducing silver ions in a solvent. Since silver particles are not inherently lyophilic, silver solution is not an example of a lyophilic colloid.

Therefore, the correct answer is 4. Silver solution.