Read the given expression. X = atomic number - number of core electrons
Which of the following explains the identity of X and its trends down a group?
OX is the effective nuclear charge, and it remains constant down a group.
OX is the screening constant, and it remains constant down a group.
O x is the effective nuclear charge, and it increases down a group.
OX is the screening constant, and it increases down a group.

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.

Nthis lab, you will do experiments to identify types of changes. using the question format you learned (shown above), write an investigative question that you can answer by doing these experiments

Which of these describes how heat is transferred by convection* a. sunlight travels through space without the aid of fluids or solids. b. warm air rises and takes the heat with it, eventually, it cools and sinks c. air at the equator rises and sinks at the poles. d. air molecules touch the warm ground, heating them up *not conduction