Final answer:
Brownian motion refers to the random motion of particles in fluids due to thermal molecular collisions, first observed by Robert Brown (Option B).
Step-by-step explanation:
Brownian motion describes the random motion of particles suspended in gases or liquids, which is observable under a microscope. This phenomenon, first directly evidenced by Scottish botanist Robert Brown in 1827 when he observed pollen grains in water, is a key element in confirming the existence of atoms. The seemingly erratic motion of these particles is due to statistical fluctuations in the number of fluid molecules colliding with the suspended particles, causing them to move in complex paths.
Brownian motion is identified as a chaotic random motion, influenced by the thermal activities of the molecules within the fluid. Despite its unpredictability on a small scale, when examining large numbers of particles, scientists can calculate meaningful information, such as the size of molecules. Hence, Brownian motion is not just random; it provides crucial insights into the kinetic behavior of molecules in fluids.
Thus, the correct option is B.