Gold numbers of some colloids are: Gelatin: 0.005 - 0.01: Gum Arabic: 0.15 - 0.25; Oleate: 0.04 - 1.0; Starch: 15 - 25. Which among these is a better protective colloid?

Gold number measures the protective power of different colloids. It is a minimum mass in mg of the dry protective colloid which will check the coagulation of 10 mL of a standard red gold sol on adding 1 mL of 10% sodium chloride solution. A better protective colloid requires minimum gold number. Hence, gelatin is the better protective colloid.