If you think at molecules, yes; it is a principle of the kinetic theory of gases. If you think at solid-gas or liquid-gas colloids, powders in gases, mist, etc. it is possible but not mandatory.
By the sun
yes they do
Since they collide at very high energies, it is expected that they will produce some new particles, that were not yet observed previously.
Yes their collision in space cause them to pick up weight when magnetised. Gas forms into an odour,so once it collides t forns an odour.