Fick’s law in transport phenomena relates to which physical process in fluids or solids?

Introduction / Context:
Fick’s law is a cornerstone of mass transfer. It states that diffusive flux is proportional to the negative gradient of concentration, analogous to Fourier’s law for heat conduction.

Concept / Approach:
Fick’s first law: J = −D * (dC/dx), where J is molar flux by diffusion, D is the diffusivity, and dC/dx is the concentration gradient. Fick’s second law accommodates transient diffusion by combining the first law with the continuity equation. These do not address particle size, feed size, or energy in crushing; they govern molecular transport in gases, liquids, and solids.

Why Other Options Are Wrong:
Energy/particle size items belong to comminution, not mass diffusion.

Final Answer:
None of these (it describes molecular diffusion)