Fick's Law Identifies Inverse Diffusion Factors

Steps:

• Recall Fick's law: diffusion rate ∝ (surface area × concentration gradient) / (distance × molecule size).
• Note factors inversely proportional to rate: distance and molecule size.
• Examine options for pair where both factors reduce rate when increased.
• Identify option A as matching both inverse factors.

Why A is correct:

• Fick's law states rate is inversely proportional to distance (longer path slows diffusion) and molecule size (larger molecules diffuse slower via lower diffusion coefficient).

Why the others are wrong:

• B: Size is inverse, but concentration gradient is directly proportional (higher gradient speeds diffusion).
• C: Both concentration gradient and surface area are directly proportional (increase rate).
• D: Surface area is directly proportional, while distance is inverse.

Final answer: A