Task: Instance Description Understanding (ontology: Earth_Environment/SWEET)

Which of the following definitions best describes the instance 'retardation factor'?

A. A relationship between the advective and diffusive components of solute transport expressed as the ratio of the product of the average interstitial velocity, times the characteristic length, divided by the coefficient of molecular diffusion; small values indicate diffusion dominance, large values indicate advection dominance.
B. In Raman spectroscopy, the instance is the intensity ratio between the perpendicular component and the parallel component of the Raman scattered light.
C. The ratio of the average linear velocity of groundwater to the velocity of the retarded constituent at C/Co=0.5.
D. The volume of water released from or taken into storage per unit volume of the porous medium per unit change in head.

Answer: The ratio of the average linear velocity of groundwater to the velocity of the retarded constituent at C/Co=0.5.