(I) Hydrogen accounts for about 73% of the observed
mass of the universe and is the most common element
in the universe. (II) Spectroscopes reveal that hydrogen
exists in the Sun and in most, if not all, other stars.
(III) Most scientists believe that hydrogen atoms were
the first atoms to form in the early universe and that the
atoms of the other elements formed later from the
hydrogen atoms. (IV) Scientific experiments show that
about 90% of the atoms in the universe are hydrogen,
about 9% are helium, and all the other elements
account for less than 1%. (V) Under such extreme
pressures, hydrogen was found to act like a metal by,
for example, conducting electricity and reflecting light.