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 each statement one by one.

### Step 1: Analyze Statement 1
**Statement 1**: "Higher the gold number of lyophilic sol, better is its protective action."

- The gold number is a measure of the protective action of a lyophilic colloid towards a lyophobic colloid.
- A lower gold number indicates better protective action because it means that less lyophilic colloid is needed to prevent coagulation of the lyophobic colloid.
- Therefore, this statement is **incorrect**.

### Step 2: Analyze Statement 2
**Statement 2**: "Lower the gold number of a lyophilic sol, better is its protective action."

- As established, a lower gold number indeed means that the lyophilic colloid has a better protective action on the lyophobic colloid.
- Thus, this statement is **correct**.

### Step 3: Analyze Statement 3
**Statement 3**: "The Brig-Arc method is usually suitable for preparing sol of inert metals."

- The Brig-Arc method is a technique used to prepare colloidal solutions of metals such as gold, silver, and platinum, which are considered inert metals.
- Therefore, this statement is **correct**.

### Step 4: Analyze Statement 4
**Statement 4**: "The osmotic pressure method gives the average molar mass of a polymer."

- The osmotic pressure method can indeed be used to determine the average molar mass of polymers using the formula:
\[ \Pi = RTC \frac{M_N}{1 + BC^2} \]
where \(\Pi\) is the osmotic pressure, \(R\) is the gas constant, \(T\) is the temperature, \(C\) is the concentration, and \(M_N\) is the average molar mass.
- Thus, this statement is **correct**.

### Conclusion
After analyzing all four statements, we conclude that the **incorrect statement is Statement 1**: "Higher the gold number of lyophilic sol, better is its protective action."

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