Question

Gold number is minimum in case of
A.Gelatin
B.Egg albumin
C.Gum Arabic
D.starch

Answer 1

First we need to know what we mean by gold number. Gold Number is the minimum weight which is expressed in milligrams of a protective colloid required to prevent the coagulation of $10mL$ of a standard hydro gold sol when $1mL$ of a $10\%$ sodium chloride solution is added to it. The gold number is inversely proportional to the protective power of the lyophilic colloid.

Complete answer:
As we know the extent of protection shown by lyophilic colloid is given by the value of its gold number.
More is the gold number, less will be the protective power of the lyophilic colloid since it means that more amount of colloid is required to prevent coagulation.
Gelatin has a gold number of $0.005 - 0.01$
Egg albumin has a gold number of $0.15 - 0.25$
Starch has a gold number of $20 - 25$
Gum arabic’s gold number is $0.15 - 0.25$
Gelatin has the lowest gold number hence it is the best protecting colloid.

Hence we can say that the correct answer is A

Additional information:
Gold number was first used by Richard Adolf Zsigmondy.
An electrical double layer is usually present on the gold sol particles which results in electrostatic repulsion between the particles. The sodium chloride ions can disrupt this electrical double layer which causes the coagulation to occur. The coagulation of gold sol results in an increase in particle size which is indicated by a color change from red to either blue or purple.

Note: The gold numbers are useful but as very rough indices of the relative protective powers this is because the gold number of a given protective colloid depends upon many conditions. The gold number of the gelatins studied was compared with the hydrogen-ion concentration, bacterial count, ash and moisture content, swelling strength, solubility, gel strength and jelly value.