Q. Illustration what is the cause of Brownian motion?
Answer:-
Molecules in a gas move freely, randomly, constantly in all directions and at high speeds. They are capable to do so for the reason that the intermolecular force of attraction between the molecules is insignificant when in a gaseous state. This steady motion of the molecules causes them to collide with anything in their path. For instance dust particles will be bombarded by the molecules travelling at high speeds causing them to have a zigzag motion. Brownian motion as well takes place in molecules in a liquid however to a less obvious extent than in a gas.