Question

The coagulation of 100 mL of a colloidal solution of gold is completely prevented by addition of 0.25 gm of a substance "X" to it before the addition of 1 mL of a 10% NaCl solution. The gold number of "X" is :

• A. 0.25
• B. 2.5
• C. 25
• D. 250

Answer 1

The correct option is C 25

Gold number is defined as number of milligrams of protective colloid added to 10 mL of colloidal gold solution to prevent its coagulation on addition of 1 mL of 10% NaCl solution.
In this question, the protective colloid "X" is added to a 100 mL solution is 250 mg i.e. 25 mg per 10 mL. Therefore, the gold number of "X" will be 25.