Adsorption of a gas on a surface follows Freundlich adsorption isotherm. Plot of log $${x \over m}$$ versus log p gives a straight line with slope equal to 0.5, then:

( $${x \over m}$$ is the mass of the gas adsorbed per gram of adsorbent)

Among the following, correct statement is :

The Tyndall effect is observed only when following conditions are satisfied:
(a) The diameter of the dispersed particles is much smaller than the wavelength of the light used.
(b) The diameter of the dispersed particle is not much smaller than the wavelength of the light used.
(c) The refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude.
(d) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.

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 ?