Gold number of gum arabic is `0.15.` The amount of gum arabic required to protect 100 mL of red gold sol from coagulation by 10 mL of `10%` NaCl solution is

Options

A. `0.15` milimoles
B. `0.15` mg
C. `1.5` millimoles
D. `1.5` mg

Explanation

To solve the problem, we need to determine how much gum arabic is required to protect 100 mL of red gold sol from coagulation when 10 mL of a 10% NaCl solution is added. We are given that the gold number of gum arabic is 0.15.

### Step-by-Step Solution:

1. **Understand the Gold Number**:
The gold number indicates the amount of protective colloid (in this case, gum arabic) required to prevent the coagulation of a certain volume of gold sol when a specific volume of an electrolyte (like NaCl) is added. Here, the gold number of gum arabic is 0.15, which means 0.15 grams of gum arabic is needed to protect 10 mL of gold sol from coagulation by 1 mL of a 10% NaCl solution.

2. **Calculate the Amount for 10 mL of Gold Sol**:
Since the gold number is given for 10 mL of gold sol, we can directly use this information. For 10 mL of gold sol, we need 0.15 grams of gum arabic.

3. **Calculate the Amount for 100 mL of Gold Sol**:
To find out how much gum arabic is needed for 100 mL of gold sol, we can use a simple proportion. If 0.15 grams is needed for 10 mL, then for 100 mL, we can set up the following calculation:
\[ \text{Amount of gum arabic} = \left(\frac{0.15 \, \text{grams}}{10 \, \text{mL}}\right) \times 100 \, \text{mL} \]

4. **Perform the Calculation**:
\[ \text{Amount of gum arabic} = 0.15 \times 10 = 1.5 \, \text{grams} \]

5. **Final Result**:
Therefore, the amount of gum arabic required to protect 100 mL of red gold sol from coagulation is **1.5 grams**.