On addition of one ml solution of `10% NaCl` to 10 ml gold solution in the presence of `0.009` g of an
anticoagulant, the coagulation is prevented. What is the gold number of anticoagulant?

Answer

To find the gold number of the anticoagulant, we will follow these steps:

### Step 1: Understand the Definition of Gold Number
The gold number is defined as the minimum weight in milligrams of a protective colloid (anticoagulant) required to prevent the coagulation of 10 ml of a standard gold solution when 1 ml of a 10% NaCl solution is added.

### Step 2: Identify Given Values
From the question, we have:
- Volume of gold solution = 10 ml
- Volume of NaCl solution = 1 ml
- Concentration of NaCl solution = 10%
- Mass of anticoagulant = 0.009 g

### Step 3: Convert Mass of Anticoagulant to Milligrams
Since the gold number is expressed in milligrams, we need to convert the mass of the anticoagulant from grams to milligrams:
\[ 0.009 \text{ g} = 0.009 \times 1000 \text{ mg} = 9 \text{ mg} \]

### Step 4: State the Gold Number
The gold number is the amount of anticoagulant required to prevent coagulation. Since we have determined that 0.009 g (or 9 mg) of the anticoagulant is sufficient to prevent coagulation in the given conditions, we can conclude:
\[ \text{Gold Number} = 9 \text{ mg} \]

### Final Answer
The gold number of the anticoagulant is **9 mg**.

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