The primary gas that makes up the universe is hydrogen. Accounting for about 75% of the elemental mass of the universe, hydrogen is the simplest and most abundant element, primarily existing in stellar gases and forms the building blocks for more complex elements through nuclear fusion in stars. In addition to hydrogen, helium is also a significant component, making up about 24% of the universe's mass. Understanding the distribution of hydrogen and other elements is crucial in cosmology, as it informs scientists about the formation and evolution of galaxies, stars, and planetary systems over billions of years.