Hydrogen is a non-metal element that is a gas at room temperature. It is used in combination with other elements to create liquid compounds such as hydrochloric acid, ammonia and hydrogen peroxide, and it combines with the element oxygen to form water. Hydrogen is also used in a liquid form with liquid oxygen to manufacture outstanding rocket fuel.
Hydrogen has a density of 0.00008988 grams per cubic centimeter, and it is likely to make up 90 percent of the visible universe. The element hydrogen consists of a one electron and one proton, and it is the most commonly found element in the universe. Most stars in the universe rely on hydrogen to produce energy through a process called "fusion."