Naturally occurring boron (B) contains 80.0% 11B (11.01 amu) and 20.0% 10B (10.01 amu). Calculate the average atomic mass of boron in amu. (10.81 amu)

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.