If gold number of A, B, C and D are 0.005, 0.05, 0.5 and 5 respectively, then which of the following will have the greatest protective value?

The minimum milligrams of protective colloid required to prevent the coagulation of10ml of gold sol by the addition to 1ml of 10% NaCl solution is called Gold number           Order of  Gold number is D>C>B>A    Order of protective power is D