0.02 g of gelatin is required to protect 10 mL of gold sol from `10% NaCl`, then find the gold number for gelatin. Report your answer by multiplying by 100.

Explanation

To find the gold number for gelatin, we will follow these steps:

### Step 1: Understand the formula for gold number
The gold number (G) is calculated using the formula:
\[ G = \frac{\text{Amount of lyophilic colloid (in mg)}}{\text{Volume of lyophobic colloid (in mL)}} \times 10 \]

### Step 2: Convert the mass of gelatin to milligrams
We are given that the amount of gelatin is 0.02 g. To convert grams to milligrams:
\[ 0.02 \, \text{g} = 0.02 \times 1000 \, \text{mg} = 20 \, \text{mg} \]

### Step 3: Identify the volume of the gold sol
The volume of the gold sol is given as 10 mL.

### Step 4: Substitute the values into the formula
Now, we can substitute the values into the formula:
\[ G = \frac{20 \, \text{mg}}{10 \, \text{mL}} \times 10 \]

### Step 5: Calculate the gold number
Now, perform the calculation:
\[ G = \frac{20}{10} \times 10 = 2 \times 10 = 20 \]

### Step 6: Multiply the result by 100
Finally, we need to multiply the gold number by 100 as per the question:
\[ \text{Gold number} = 20 \times 100 = 2000 \]

### Final Answer
The gold number for gelatin is **2000**.

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