`5ml` of standard gold sol, needs `0.5 mg` of gelation for its protection from coagulation, calculate the gold no of gelation.

Options

A. 1
B. 2
C. 3
D. 4

Explanation

To calculate the gold number of gelatin based on the given data, we can follow these steps:

### Step 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 standard gold sol when 1 ml of a 10% NaCl solution is added.

### Step 2: Identify the Given Data
From the problem, we know:
- Volume of gold sol = 5 ml
- Amount of gelatin needed for 5 ml of gold sol = 0.5 mg

### Step 3: Calculate the Amount of Gelatin Needed for 10 ml
Since the amount of gelatin required is proportional to the volume of the gold sol, we can set up a proportion to find out how much gelatin is needed for 10 ml of gold sol.

Using the formula:
\[ \text{Amount of gelatin for 10 ml} = \left(\frac{\text{Amount of gelatin for 5 ml}}{5 \text{ ml}}\right) \times 10 \text{ ml} \]

Substituting the values:
\[ \text{Amount of gelatin for 10 ml} = \left(\frac{0.5 \text{ mg}}{5 \text{ ml}}\right) \times 10 \text{ ml} \]

### Step 4: Perform the Calculation
Calculating the above expression:
\[ \text{Amount of gelatin for 10 ml} = \left(0.1 \text{ mg/ml}\right) \times 10 \text{ ml} = 1 \text{ mg} \]

### Step 5: State the Gold Number
The gold number of gelatin is therefore 1 mg, which means 1 mg of gelatin is required to prevent coagulation of 10 ml of standard gold sol upon the addition of 1 ml of 10% NaCl solution.

### Final Answer
The gold number of gelatin is **1**.

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