Atoms of different elements always combine in compounds

Which of the following signs of a chemical reaction are observed in the reaction of potassium with water? precipitate formed temperature change smell produced gas produced color change

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 does the field of thermodynamics relate to a-changes in nuclear reactions b- changes in energy in systems c changes in molecular structure d changes in atomic properties