On addition of 1 ml solution of 10% NaCl to 10 mL gold sol in the presence of 0.025 g of starch, the coagulation is just prevented. Starch has the gold number

Options

A. 0.025
B. 0.25
C. 0.5
D. 25

Answer

D

Explanation

By definition, gold number of starch is the amount of starch in mg added to 10 mL standard gold sol which prevents the coagulation of gold on adding 1 mL of 10% NaCl solution. The amount of starch is 0.025 g = 25 mg. Hence, gold number is 25.