Final answer:
Hydrogen is the lightest and most abundant element in the universe, essential for star formation and life on Earth. It comprises about 70%-75% of the universal mass and plays a crucial role in compounds such as water and organic molecules.
Step-by-step explanation:
The lightest and most abundant element and considered the fuel of the universe is Hydrogen (C). Hydrogen is central to the process of nucleosynthesis, where it's believed that all other elements were originally formed from a series of nuclear reactions beginning with hydrogen. Hydrogen makes up about 70%-75% of the universe by mass and is essential in the fusion reactions that power stars. This element is found in many compounds, including water (H2O), and is a component of numerous carbon-containing compounds critical for life such as cellulose, starch, sugars, fats, alcohols, and many more.
Not only is hydrogen a significant part of the composition of stars, but also it plays a critical role in the chemical makeup of living organisms. Elements like carbon, nitrogen, and oxygen, which are common in the universe, combine with hydrogen to form various compounds necessary for life. Moreover, terrestrial hydrogen is mostly found in water molecules and organic compounds due to its reactivity and low density.