On addition of one mL solution of `10%` NaCl to 10 mL gold sol in the presence fo `0.0250` g of starch, the coagulation is just prevented. Starch has the following gold number

Options

A. 0.025
B. 0.25
C. 0.5
D. 250

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. So the amount of starch is 0.25g = 250 mg. Hence gold number is 250.