It takes only one atom to make hydrogen; however, hydrogen is commonly found as H2, meaning two atoms make up hydrogen. Because of this, hydrogen is known as a diatomic element.
Hydrogen is the lightest element, has an atomic number of 1 and uses the symbol H. At standard temperature and pressure, hydrogen is an odorless and colorless gas. It is combustible and produces water when it burns in air.
Hydrogen is also the most abundant element in the universe, with 90 percent of atoms in the universe being made of hydrogen. Main sequence stars, such as the sun, burn hydrogen as fuel.