Earlier the term 'Colloids' was used for a category of substances. However, later, the term colloidal state of matter was preferred. Colloidal dispersions have been classified into different types depending upon the physical state of the dispersed phase and the dispersion medium or the nature of the colloidal particles. They are prepared in the industry or in the laboratory by a number of methods and then purified. Their property has also been studied in detail. Hardy and Schulze made a substantial contribution in studying the coagulation of the colloidds. The protective action of lyophilic colloids was studied by Zsigmondy and he introduced a term, called 'gold number'.

Which of the following has minimum gold number?

Gelatine

The correct answer is option 3. Gelatine.

The gold number is a measure used to compare the protective power of different colloids. It is defined as the minimum amount of colloid (in milligrams) required to prevent the coagulation of 10 mL of a gold sol when 1 mL of a 10% sodium chloride solution is added. The gold sol, which is a suspension of tiny gold particles, will coagulate and form a visible precipitate when destabilized by the addition of an electrolyte like sodium chloride. A protective colloid prevents this coagulation by stabilizing the gold particles.

The lower the gold number, the more effective the colloid is at stabilizing the gold particles, indicating a higher protective power. Here’s how each of the given substances typically ranks in terms of gold number:

1. Potato starch: Starch has a moderate protective power, with a gold number usually around 20-25.

2. Gum arabic: Gum arabic has a relatively good protective power, with a gold number around 0.1-0.2.

3. Gelatine: Gelatine is known to have an excellent protective power, with a gold number around 0.005-0.01.

4. Albumen: Albumen (egg white) also has a good protective power, with a gold number around 0.1.

Therefore, among these substances, gelatine has the lowest gold number, typically in the range of 0.005-0.01. This means that gelatine requires the smallest amount to prevent the coagulation of the gold sol, demonstrating its high protective capability.

Thus, gelatine has the minimum gold number among the options provided, indicating it is the most effective at protecting gold nanoparticles from coagulation.