Which of the following observations would indicate that a material is a pure substance?
it does not dissolve in water.
it changes color after heating,
it cannot be physically broken down into different types of atoms.
it can be physically broken down into different types of molecules

Which statement is a reason to support population regulation? a) it is unethical for us to control birth control rates b) humans have the freedom to produce as many children as desired c) the gap between the rich and poor has been narrowing since 1960 d) billions more people on the earth will intensify many environmental and social problems

Check the correct box to describe the periodic trends in electronegativity. electronegativity across a period: decreases. increases. electronegativity down a group: decreases. increases.

How many neutrons does a atom of cobalt have?