Why do group 7 elements have higher melting and boiling points going down?

Transportation is the largest single source of air pollution in the united states. air pollution can harm the environment and human health. which technology could offer a solution to this problem? mufflers that reduce noise motors that run on electricity tires that improve gas mileage

Why doesn't heat added to water make the tempature rise above 100c

Which part of earth’s surface receives the most direct rays from the sun? a) equator b) ocean c) poles d) mountains