Question

On the addition of 1 ml. of 10% solution of sodium chloride to 10 ml. of gold sol in presence of 0.025 g of starch, the coagulation is just prevented. The gold number of starch is

• A. 0.025
• B. 0.25
• C. 2.5
• D. 25

Answer 1

The correct option is A

0.025

Minimum mass (mg) of lyophilic sol to be added to 10 ml of gold sol which can prevent from coagulation on addition upon 1 ml of 10% NaCl solution is called gold number which is 0.025 in this case.