on addition of 1 ml solution of `10% NaCl` to 10 ml gold sol in the presence of 0.25g of strach, the coagulation is just prevented. Strach has the following gold number

Options

A. 25
B. 0.025
C. 0.25
D. 2.5

Explanation

Gold number of a protective colloid is the minimum weight of it in milligrams which must be added to 10 ml of a standard red gold sol so that no coagulation of the gold sol takes place when 1 ml of 10% sodium chloride solution is rapidly added to it.