What is the most abundant element in the universe?

Hydrogen is the most abundant element in the universe, comprising about 75% of its elemental mass. This abundance is primarily a result of the processes that occurred shortly after the Big Bang, when the universe was still forming. In its early stages, hydrogen atoms were formed from the cooling and expansion of energy, and since then, they have been fundamental in the formation of stars and galaxies.

As the universe evolved, hydrogen continued to play a critical role in stellar processes, including nuclear fusion, which occurs in stars. In these stellar environments, hydrogen is fused to create heavier elements, but hydrogen remains the most prevalent due to its pivotal role as a building block for stars.

In contrast, while elements like oxygen and carbon are also significant in the universe, they are formed in smaller quantities through stellar nucleosynthesis and are not nearly as abundant as hydrogen. Helium, while the second most abundant element, makes up a significantly smaller portion of the universe compared to hydrogen. Therefore, the recognition of hydrogen as the most abundant element is rooted in both its historical formation and its ongoing role in the cosmos.