Q. The coagulation of $10\ {cm}^{3}$ of gold sol is completely prevented by addition of 0.025 g of starch to it. The gold number of starch is
A) 0.025
B) 0.25
C) 2.55
D) 25
Explanation
(d)
Gold number is the amount of substance in milligram that is required to prevent coagulation of $10\ {cm}^{3}$ of gold sol by addition of $1\ mL\ of\ 10\%\ NaCl$ solution.
Convert 0.025 g into milligram = 25
$0.025\ g\ starch = 0.025 \times 1000 = 25\ mg$
Thus, the gold number of starch = 25
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.