Answer the question on basis of passage given below:

Lyophobic sols like those of metals (Au, Ag, etc) are unstable and are easily precipitated by addition of electrolytes. However, it is observed that the addition of certain lyophilic colloids like gums, soaps, gelatine, etc. to lyophobic colloids (like a metal sol) render lyophobic colloids difficult to coagulate by the addition of electrolytes. The process is known as 'protection' and the lyophilic colloids are termed as Protective colloids. It is believed that the protective action of the lyophilic colloids is due to the covering up of the particles of the lyophobic colloid by those of the lyophilic colloid. Evidently, smaller the gold number of a protective colloid, the greater is its protective action.

Evidently, smaller the gold number of a protective colloid, the greater is its protective action. In which of the following sols, the colloidal particles will move towards the cathode during electrophoresis?

\(Fe(OH)_3\) sol

The correct answer is option 1. \(Fe(OH)_3\) sol.

The Gold Number is a measure of the protective power of a protective colloid. It indicates the minimum amount of electrolyte needed to cause coagulation of a given weight of gold sol. A lower Gold Number signifies greater protective action of the colloid.

During electrophoresis, colloidal particles move towards the oppositely charged electrode. Since the cathode is negatively charged, colloidal particles with positive charges or with a higher affinity for negative charges will move towards the cathode.

Let's analyze the options:

1. \(Fe(OH)_3\) sol: Iron(III) hydroxide sol particles are positively charged due to the hydrolysis of \(Fe^{3+}\) ions in water. Therefore, they would move towards the cathode during electrophoresis.

2. \(Au\) sol: Gold sol particles are negatively charged, so they would move towards the anode during electrophoresis.

3. Starch sol: Starch molecules are generally neutral or negatively charged. Therefore, they may not move significantly during electrophoresis.

4. \(As_2S_3\) sol: Arsenic sulfide sol particles are negatively charged, so they would move towards the anode during electrophoresis.

Based on the analysis, the only option where the colloidal particles will move towards the cathode during electrophoresis is: (1) \(Fe(OH)_3\) sol