The coagulation of `100 mL` of a colloidal solution of gold is completely prevented by the addition of `0.030 g` of it before adding `1 mL` of `10% NaCl` solution. Find out the gold number of starch?

Explanation

To find the gold number of starch, we need to 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 (in this case, starch) 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: Calculate the Amount of Starch for 10 mL of Gold Sol
We know that 0.030 g of starch is sufficient to prevent coagulation in 100 mL of the colloidal solution. To find out how much starch is needed for 1 mL, we can use the following calculation:

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