Helium and hydrogen are two of the most abundant gases in the universe. They are both colorless, odorless, and non-toxic. Helium is the second most abundant element in the universe, and it is the lightest of all the elements. Hydrogen is the most abundant element in the universe, and it is the simplest and lightest of all the elements. Both gases are used in a variety of applications, including rocket fuel, welding, and medical imaging.