Which two elements are the most abundant in the chemical composition of the universe?

The most abundant elements in the chemical composition of the universe are hydrogen and helium. This stems from the conditions present during the Big Bang, which caused the formation of these elements in large quantities.

Hydrogen, being the simplest and lightest element, constituted about 75% of the normal matter in the universe, while helium accounts for about 24%. Together, they form the majority of the visible universe's elemental makeup. The relative abundance of these elements is crucial for the development of stars and galaxies, as stars primarily fuse hydrogen into helium during their life cycles.

Other elements, such as carbon, nitrogen, and oxygen, were formed later in the interiors of stars through nuclear fusion processes and are significantly less abundant when considering the universe as a whole. Therefore, hydrogen and helium are correctly identified as the most abundant elements in the universe's chemical composition.