Question

The Brownian movement is due to:
A. Temperature fluctuations within the liquid phase
B. Attraction and repulsion between charges on colloidal particles.
C. Impact of molecules of the dispersion medium on colloidal particles
D. Convection currents

Answer 1

If you look at the sunlight from a hole or coming from a window, you would notice that it has dust particles in it which are shining as they reflect light but you will also notice that they are not moving in straight line rather they are forming a zig-zag motion which is known as Brownian motion.

Complete step by step process:
Brownian motion is the zig-zag movement of colloidal particles in colloidal solution. It is the result of agitation of molecules in fluid due to kinetic energy in those molecules and then they strike the colloidal particles with full force from opposite directions and hence, that results in the zig-zag motion. If a fluid is less viscous than it would show a strong force of hit to the colloidal particles. The molecules which have diameter less than 1 mu are rarely observed as the particles of the fluid would be bigger than the dispersed phase.
The Diffusion coefficient can be expressed with the Stokes-Einstein equation:
${{D}_{{}^\circ }}=\dfrac{{{k}_{B}}T}{6\pi \eta r}$
Where, ${{D}_{{}^\circ }}$ is the diffusion coefficient
${{k}_{B}}$ is Boltzmann’s constant
T is the absolute temperature
$\eta$ is the viscosity
R is the radius of a spherical particle.

Note: As we can see in the above stated formula that Brownian motion does not depend on the nature of the colloid but does depend on the size of the colloid and viscosity of the solution. The less viscous the fluid is, more will be the movement of the particles.