The method used in this experiment is difficult to apply for determining the formula weight of unknown salts in aqueous solutions. Even when accurate freezing point depressions are measured, the results are not always conclusive because there can be an undetermined parameter. Considering the information in the Introduction section, what is the best explanation for this difficulty?

15. which of the following is not human-caused groundwater pollution? a. water in an aquifer dissolves elements such as arsenic and mercury from surrounding rock. b. water in an aquifer is contaminated by leachate that seeps into the ground from a landfill. c. water in an aquifer becomes polluted with chemicals used in hydraulic fracturing, or fracking. d. water in an aquifer absorbs harmful bacteria from the drainage field of a septic tank.