(a) Diffusion takes place most rapidly in gasses. The particles of gas have more kinetic energy due to that they move with high speed. Because of the movement of particles with high speed gas diffuses most rapidly.

(b) Carbonated drinks are prepared by the diffusion of gas in water(liquid). We notice a hiss sound when the cap of bottle of a carbonated drink is open, the hiss sound comes because of the diffused gas coming out of water. Soda, Soft drinks are the carbonated drinks and prepared mainly because of the diffusion of carbon dioxide in water(liquid).