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 ?

Question

$\begin{array}{11}(1) Gelatin\\ (2) Gum\; Arabic\\ (3) Oleate \\(4) Starch \end{array} $