Which statement is incorrect ?

Options

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

Answer

To determine which statement is incorrect regarding the protective action of lyophilic sols and the concept of gold number, we can analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Gold Number**:
- The gold number is defined as the minimum mass of a colloid (in milligrams) that is required to protect 10 ml of a red gold sol from coagulation when 1 ml of 10% NaCl is added.
- It is important to note that the lower the gold number, the better the protective action of the colloid.

2. **Analyzing the Statements**:
- **Statement 1**: "Higher the gold number of lyophilic sol, better is its protective action."
- This statement is incorrect because a higher gold number indicates a lower protective action. Thus, the protective action is better when the gold number is lower.

- **Statement 2**: "Lower the gold number of lyophilic sol, better is its protective action."
- This statement is correct. As explained, a lower gold number correlates with better protective action.

- **Statement 3**: "Bridge arc method is usually suitable for preparing sols of inert metals."
- This statement is correct. The bridge arc method is indeed used to prepare colloidal solutions of inert metals such as gold, silver, and platinum.

- **Statement 4**: "The osmotic pressure method gives the average molar mass of polymer."
- This statement is also correct. The osmotic pressure method can be used to determine the average molar mass of polymers.

3. **Conclusion**:
- The only incorrect statement among the options provided is **Statement 1**.

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

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