Give the definition for diffusion.

(a) gas molecules mix unequally average distance between collisions
(b) gas molecules escape from a container into a vacuum through a small hole
(c) gas molecules mix equally
(d) gas molecules spread out in a concentration gradient

option D.  

Explanation:

The correct answer is option D.                

Diffusion is the particle movement from high concentration to low concentration, such as air, water, etc.                      

Example: if you spray perfume spread throughout the room at one part of the fragrance scent.                                                        

The gas molecule thus spreads out in a gradient of concentration

conduction, convection, radiation