Question:

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

Starch

Oleate

Gum Arabic

Gelatin

Gold number ∝ 1/Protective power
Therefore, a gold number of Gelatin is the lowest among the above and hence is a better protective colloid.