Hydrogen is the most common element in the universe, making up about 75% of its elemental mass. It is the simplest and lightest element, consisting of one proton and one electron. Hydrogen plays a crucial role in the formation of stars and galaxies, as it serves as the primary fuel for stellar nuclear fusion. In stars, hydrogen atoms fuse together to create helium, releasing vast amounts of energy in the process. This process not only powers stars but also creates the elements necessary for life. Hydrogen's abundance and its fundamental role in the cosmos make it a key subject of interest in astrophysics and cosmology.