the protective power of the lyophilic colloids es expressed in terms of gold number, a term introduced by Zsigmondy. Gold number is the number of milli - gram of the protective colloid which prevent the coagulation of 10 mLof red gold sol , when 1 mL of a 10 per cent solution of sodium chloride is added to it . thus smaller the gold number of lyophillic colloid, the greater is the protective power.
On addition of one mL of sloution of 10 % NaCl to 10 mL. of red gold sol in presence of 0.025 g of starch the coagultion is just prevented . the gold number of starch is

Options

A. 0.025
B. 0.25
C. 2.5
D. 25

Answer

To find the gold number of starch, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Gold Number**:
The gold number is defined as the amount of protective colloid (in milligrams) required to prevent the coagulation of 10 mL of a red gold sol when 1 mL of a 10% sodium chloride solution is added.

2. **Identify the Given Data**:
In this case, we are given that 0.025 g of starch is used to prevent coagulation. We need to convert this mass into milligrams for our calculation.

3. **Convert grams to milligrams**:
Since 1 g = 1000 mg, we can convert 0.025 g to milligrams:
\[ 0.025 \, \text{g} = 0.025 \times 1000 \, \text{mg} = 25 \, \text{mg} \]

4. **Determine the Gold Number**:
According to the definition, the gold number is the amount of starch (in mg) that prevents coagulation. Since we found that 25 mg of starch is required, we conclude that:
\[ \text{Gold Number of Starch} = 25 \, \text{mg} \]

5. **Final Answer**:
Therefore, the gold number of starch is 25.