The expected answers are:

(a)Any two correct factors that can affect the rate of diffusion e.g.

-Density
-Mass
-Temperature

(b)Any correct two examples to illustrate the effects of surface tension e.g.

-soap bubbles are spherical in shape
-water skaters are able to walk on the surface of water
-clean razor blade/needle gently placed on the surface of water floats
-Spilled mercury on (clean) glass surface forms spherical droplets

This question on diffusion and surface tension was quite popular among the candidates. The performance was quite satisfactory. Most candidates were able to list the factors that affect the rate of diffusion and examples to illustrate the effects of surface tension. Some few candidates still confused the concept of diffusion with osmosis and evaporation.