The first element on the periodic table is hydrogen. It is represented by the symbol H and has an atomic number of 1. Hydrogen is the lightest and most abundant element in the universe, making up approximately 75% of its elemental mass. It exists primarily as a diatomic molecule (H2) and is a key component of stars, including our Sun, where nuclear fusion occurs. Hydrogen is vital in various chemical processes and industries, including fuel cells, fertilizers, and the production of organic compounds. Its unique properties and behavior in reactions make it fundamental to both chemistry and biochemistry.