On addition of 1 mL solution of l0% NaCl to l0 mL gold sol in the presence of 0.25 g of starch, the coagulation is just prevented. The gold number of Starch is

By definition, gold number of starch is the amount of starch in milligram added to 10 mL standard gold sol which prevents the coagulation of gold on adding 1 mL of 10% NaCl. So the amount of starch is 0.25 g = 250 gm. Hence gold number is 250.