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

Options

A. 0.25
B. 25
C. 250
D. 2.5

Answer

B

Explanation

250 mg of X is present in 100 mL of colloidal sol of gold. By definition, gold no. of X is that amount of it in mg which is present in 10 mL of colloidal gold solution. Hence in 10 mL, the amount of X present is 25 mg which is the gold number of X.