What is the most abundant element found in the universe?

Hydrogen is the most abundant element in the universe, accounting for about 75% of its elemental mass. This lightweight element plays a critical role in the structure of stars, where nuclear fusion processes convert hydrogen into helium, releasing energy that powers the stars. The prevalence of hydrogen is a fundamental aspect of the universe's chemistry and astrophysics, as it is the building block for the formation of more complex elements through stellar processes.

In contrast, while oxygen, carbon, and nitrogen are also important and abundant in specific contexts, such as in the formation of life or within certain types of stars, they do not match the overwhelming presence of hydrogen throughout the universe. Oxygen is the third most abundant element, carbon is central to organic chemistry, and nitrogen is significant in biological processes, but none of them approaches the sheer quantity of hydrogen in the cosmos. Understanding hydrogen's significance provides insight into both cosmology and the evolution of matter in the universe.