The lightest element in the periodic table is hydrogen (H). It has an atomic number of 1, indicating it consists of just one proton and one electron. Hydrogen is a colorless, odorless gas at room temperature and is the most abundant element in the universe, playing a key role in the formation of stars and molecules. In addition to being a building block of all matter, hydrogen is essential for many chemical reactions, including those involved in cellular respiration and photosynthesis. Its unique properties make it crucial in various industrial applications, including fuel cells and fertilizers.