Scientists are studying how substance a and substance b react. when substance a and b are mixed, a substance different from a and b floats to the top of the solution. this is evidence that a(n) question 6 options: a. chemical change occurred. b. irreversible change occurred. c. endothermic change occurred. d. physical change occurred.

This drawing shows a human body system. what is the primary function of this body system?

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.

Which states of matter have particles that move independently of one another with very little attraction?