Which statement is incorrect ?

Options

A. Higher the gold number of lyophilic sol better is itsprotective action
B. Lower the gold number of a lyophilic sol batter is its protective action
C. The Bredig's arc method is usually suitable for preparing sols of inert metals
D. The osmotic pressure method gives the average molar mass of a polymer

Answer

To determine which statement is incorrect, let’s analyze the statements provided in the video transcript step by step.

### Step 1: Understanding Gold Number
The first statement claims that "Higher the gold number of a lyophilic sol, better is its protective action."

**Explanation**:
- The gold number is defined as the minimum weight of protective colloid (in milligrams) required to prevent the coagulation of 10 ml of a gold sol from 10 ml of a 1% NaCl solution.
- A higher gold number indicates that more protective colloid is needed to prevent coagulation, which implies that the protective action is weaker. Therefore, this statement is **incorrect**.

### Step 2: Braddock's Arc Method
The second statement discusses Braddock's Arc Method, stating that it is usually stable for the preparation of sols of inert metals.

**Explanation**:
- The Braddock's Arc Method involves creating a colloidal solution by melting the metal and allowing it to cool rapidly, forming colloidal particles.
- This method is indeed used for preparing colloidal solutions of inert metals, making this statement **correct**.

### Step 3: Osmotic Pressure Method
The third statement mentions that the osmotic pressure method gives an average molar mass of a polymer.

**Explanation**:
- The osmotic pressure method can be used to determine the molar mass of solutes, including polymers, by measuring the osmotic pressure of a solution.
- The relationship between osmotic pressure, concentration, and temperature allows for the calculation of molar mass, making this statement **correct**.

### Conclusion
Based on the analysis:
- The first statement is incorrect: "Higher the gold number of a lyophilic sol, better is its protective action."
- The second and third statements are correct.

### Final Answer
The incorrect statement is: "Higher the gold number of a lyophilic sol, better is its protective action."

---