The gold number of gelatin is `0.01` . Calculate the amount of gelatin to be added to `1000mL` of a colloidal sol of gold to prevent its coagulation, before adding `1mL` of `10%NaCl` solution.

Options

A. 2
B. 1
C. 4
D. 5

Explanation

To solve the problem, we need to calculate the amount of gelatin required to prevent the coagulation of a colloidal sol of gold when a certain volume of NaCl solution is added. Here’s a step-by-step solution:

### Step 1: Understand the Gold Number
The gold number of gelatin is given as `0.01`. This means that `0.01 mg` of gelatin is required to prevent coagulation of `10 mL` of a colloidal gold sol when `1 mL` of `10% NaCl` solution is added.

### Step 2: Calculate the Amount of Gelatin for 1000 mL
We need to find out how much gelatin is required for `1000 mL` of the colloidal gold sol.

Using the relationship:
- `0.01 mg` of gelatin for `10 mL` of gold sol.

We can set up a proportion to find the amount of gelatin needed for `1000 mL`:
\[ \text{Amount of gelatin} = \left(\frac{0.01 \text{ mg}}{10 \text{ mL}}\right) \times 1000 \text{ mL} \]

### Step 3: Perform the Calculation
Now, we can calculate the amount of gelatin:
\[ \text{Amount of gelatin} = \left(\frac{0.01}{10}\right) \times 1000 = 0.01 \times 100 = 1 \text{ mg} \]

### Step 4: Conclusion
Thus, the amount of gelatin required to prevent coagulation of `1000 mL` of colloidal gold sol before adding `1 mL` of `10% NaCl` solution is `1 mg`.

### Final Answer
The amount of gelatin to be added is **1 mg**.

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