Which chemical element is the most abundant in the universe?

Hydrogen is the most abundant chemical element in the universe.

Hydrogen makes up roughly 75% of ordinary matter by mass and about 90% of atoms, with helium accounting for most of the remainder. This abundance comes from the Big Bang, which produced mostly hydrogen and helium in the early universe.

Stars continue to transform hydrogen into helium through nuclear fusion. In the Sun, this process releases the energy that produces sunlight and heat. Hydrogen is also present in water, organic molecules, and many other compounds on Earth.

Hydrogen should not be confused with the most abundant element in Earth’s crust or atmosphere, which depends on how the material is measured. It is also the lightest element, with one proton in its most common isotope. Molecular hydrogen normally exists as H₂, not as isolated atoms.