Hydrogen is the lightest and most abundant element in the universe, making up about 75% of its mass. It is a colorless, odorless, and highly flammable gas. It has the atomic number 1 and is symbolized by the letter H in the periodic table. Hydrogen can be found in various compounds such as water, organic compounds, and fossil fuels. It is also a key component of stars and plays a crucial role in nuclear fusion reactions. In recent years, hydrogen has gained attention as a potential renewable energy source, as it can be produced by splitting water molecules using renewable sources such as solar or wind energy.