What is Brownian motion?

Brownian motion refers specifically to the chaotic and random movement of colloidal particles suspended in a fluid (liquid or gas). This phenomenon arises due to collisions between the particles and the molecules of the surrounding medium, which are in constant motion themselves. As a result, the particles experience a jittery, erratic movement that can be observed under a microscope.

Understanding Brownian motion is crucial in various fields, such as physical chemistry, biology, and material science, as it provides insights into the behavior of particles at a microscopic level and is foundational for explaining diffusion processes. The other options do not accurately capture the essence of Brownian motion; for instance, the movement of solid particles in a solution does not encapsulate the random and chaotic nature characteristic of Brownian motion, while the stationary state of liquids and a chemical change in liquid substances refer to different physical and chemical concepts.