h

Hydrogen is a chemical element with the symbol H and atomic number 1. It is the lightest element in the periodic table and the most abundant chemical substance in the universe, constituting roughly 75% of all baryonic mass. Hydrogen exists in several forms on Earth, primarily as a gas consisting of diatomic molecules (H2). It is highly flammable and is used in various industrial applications, including the production of ammonia for fertilizers and as a fuel in hydrogen fuel cells.