The most abundant element in the universe is hydrogen. Making up approximately 75% of the elemental mass of the universe, hydrogen is the simplest and lightest element, consisting of only one proton and one electron. It plays a critical role in the formation of stars and galaxies, as hydrogen atoms fuse under immense pressure and temperature in stellar cores, producing helium and releasing vast amounts of energy. This process, known as nuclear fusion, is the foundation of stellar life cycles. In addition to its cosmic abundance, hydrogen is also essential for life on Earth, forming water and organic compounds.