Question

Relatively which conditions favour the faster Brownian movement of colloidal particles in solution?

• A. Smaller size and higher viscosity
• B. Smaller size and lesser viscosity
• C. Bigger size and higher viscosity
• D. Bigger size and lesser viscosity

Hint:

Brownian movement increases with: \[ \text{Temperature} \uparrow \] \[ \text{Particle size} \downarrow \] \[ \text{Viscosity} \downarrow \] Thus, small colloidal particles in a low-viscosity medium show the most rapid Brownian motion.

Answer 1

The Correct Option is B

Brownian motion comes from lopsided collisions, at any instant a colloidal particle gets hit slightly more from one side than the other by the fast moving molecules of the medium, and it jitters off in that direction.

Two things control how vigorous this jitter is. First, a smaller particle is easier to shove around, the same imbalance in collisions produces a bigger displacement on a light, small particle than on a heavy, bulky one.

Second, the medium itself has to let the particle move. A viscous medium resists motion and drags the particle back, damping the jitter, while a thin, low viscosity medium offers little resistance and lets the particle respond freely to every collision.

Combining both factors, the fastest Brownian movement needs a particle that is easy to push, that is small size, in a medium that does not resist that push, that is low viscosity.

So the correct choice is option (2).