hydrogen vs. helium

Hydrogen and helium are both simple, light gases found in the universe. Hydrogen is the most abundant element, made of one proton and one electron, and is highly reactive, forming water and many compounds. Helium is a noble gas with two protons and two electrons, making it very stable and unreactive. Hydrogen is flammable and used as fuel, while helium is inert, used for balloons and cooling. Both gases are key to understanding stars; hydrogen fuses into helium in stellar cores, powering the sun.