JEE Advanced levelSingle correct optionDifficulty 3 of 3sc147
The gold numbers of four protective colloids are gelatin 0.005, haemoglobin 0.03, gum arabic 0.15 and starch 25 (all in mg). Which option correctly gives the order of decreasing protective power and the ratio (mass of starch)/(mass of gelatin) needed to protect the same amount of gold sol?
A smaller gold number means a better protector, so the order is gelatin, haemoglobin, gum arabic, starch. The mass needed for the same sol is proportional to the gold number, so the ratio of masses is 25/0.005=5000.