Which chemical element is by mass the third-most abundant element in the universe after hydrogen and helium?

Explanation

Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table. It is a highly reactive nonmetal and an oxidizing agent. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. Oxygen was discovered independently by Carl Wilhelm Scheele in 1773 and Joseph Priestley in 1774. The name oxygen was coined in 1777 by Antoine Lavoisier.