0.030g of starch is required to prevent coagulation of 10 mL of gold sol when 1 mL of 10% NaCl solution is present. Thus, gold number of starch sol is

Starch sol is a protective sol. By definition of Gold number, it is the amount of protective sol in milligrams that prevents coagulation of 10 mL of gold sol on addition of 1 mL of 10% NaC solution.As per data given, starch required = 0.0300 g= 0.030x 1000 mg 30 mgThus, gold number = 30