Question

The coagulation of 100 ml of colloidal solution of gold is completely prevented by addition of 0.25 g of a substance “X” to it before adding 1 ml of 10% NaCl solution. The gold number of “X” is

• A. 0.25
• B. 25
• C. 250
• D. 2.5

Answer 1

The correct option is B 25

250 mg of X prevents coagulation of 100 ml of colloidal sol of gold. By definition, gold no. of X is that amount of it in mg which prevents coagulation of 10 ml of colloidal gold sol. Hence, to prevent coagulation of 10 ml of gold sol, the amount of X required = 25 mg, which is the gold number of X.