A difference in the concentration of a substance across a distance is known as a

• A. Energy
• B. Isotonic
• C. Dynamic equilibrium
• D. Concentration gradient

Answer: (D)

A concentration gradient is the difference in the amount of a substance from one location to another. When such a gradient exists, particles move naturally from regions of higher concentration to regions of lower concentration through diffusion. This flow continues until the concentrations become equal and the net movement stops, reaching dynamic equilibrium. An isotonic condition describes having equal solute concentrations between two solutions at a boundary, which is about balance across a boundary rather than a distance-based difference within space. Energy is a general term for the capacity to do work and does not itself describe the spatial distribution of a substance.