Which statement about Brownian diffusion is true?

Which statement about Brownian diffusion is true?

• A. It only occurs for large particles
• B. It involves random motion of very small particles causing deposition on surfaces
• C. It relies on gravity
• D. It is independent of particle size

Answer: (B)

Brownian diffusion is the random, thermal motion of tiny particles driven by collisions with surrounding molecules. This erratic movement causes ultrafine particles to wander and eventually reach and deposit on nearby surfaces, even without gravity pulling them down. That’s why the true statement describes random motion of very small particles leading to deposition on surfaces. Larger particles aren’t primarily governed by Brownian diffusion; gravity and inertia dominate their movement, so diffusion isn’t the main deposition mechanism for them. The diffusion rate also isn’t the same across all sizes—smaller particles diffuse more readily because their diffusion coefficient is larger, while bigger particles diffuse more slowly. So diffusion is strongly dependent on particle size, not independent of it. In aerosol therapy terms, this means ultrafine particles can deposit in regions where diffusion is significant, whereas larger particles settle or impact surfaces mainly through other mechanisms.

Brownian diffusion is the random, thermal motion of tiny particles driven by collisions with surrounding molecules. This erratic movement causes ultrafine particles to wander and eventually reach and deposit on nearby surfaces, even without gravity pulling them down. That’s why the true statement describes random motion of very small particles leading to deposition on surfaces.

Larger particles aren’t primarily governed by Brownian diffusion; gravity and inertia dominate their movement, so diffusion isn’t the main deposition mechanism for them. The diffusion rate also isn’t the same across all sizes—smaller particles diffuse more readily because their diffusion coefficient is larger, while bigger particles diffuse more slowly. So diffusion is strongly dependent on particle size, not independent of it.

In aerosol therapy terms, this means ultrafine particles can deposit in regions where diffusion is significant, whereas larger particles settle or impact surfaces mainly through other mechanisms.