Black holes cannot be seen. However, scientists think that black holes exist because of their effect on surrounding matter. Describe another force or phenomenon that cannot be seen directly. Give examples of the effects of this force on everyday objects.

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.

What is the chemical formula of magnesium bromide? a. mgbr2 b. mgbr c. mg2br2 d. mg2br

What is the balance to the equation?