75% of the matter in the universe is hydrogen.
The most abundant is hydrogen, a chemical element represented by the symbol H and with an atomic number of 1. Under normal conditions of pressure and temperature hydrogen is an odourless, colourless, tasteless, non-metallic and highly flammable diatomic gas (H2). With an atomic mass of 1.00794(7) u, hydrogen is the lightest chemical element and is also, as noted at the beginning, the most abundant element, constituting about 75% of the matter in the universe, mainly in stars and interstellar clouds.
SOME FACTS ABOUT HYDROGEN, THE MOST ABUNDANT ELEMENT IN THE UNIVERSE
Atomic number (number of protons in the nucleus): 1
Atomic symbol (in the Periodic Table of Elements): H
Atomic weight (mean mass of the atom): 1.00794
Density: 0.00008988 grams per cubic centimeter
Phase at room temperature: Gas
Melting point: minus minus 259.34 degrees Celsius
Boiling point: minus 252.87 C
Number of isotopes (atoms of the same element with a different number of neutrons): 3 common isotopes, of which 2 are stable.
Most common isotope: 1H, natural abundance 99.9885 percent.
