How could you use existing elements to make a Helium atom?

Select all of the statements which are true. electrons are located in shells or orbits around the atom. electrons orbit slowly around the atom. electrons travel in one flat path around the nucleus of an atom. the valence of an atom is determined by the number of electrons in the atom's outermost shell.

What does the symbol (–hfus) indicate in a phase change?

What are the two largest greenhouse gases