Hydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms (most of the mass of the universe, however, is not in the form of chemical-element type matter, but rather is postulated to occur as yet-undetected forms of mass such as dark matter and dark energy). This element is found in great abundance in stars and gas giant planets. Molecular clouds of H2 are associated with star formation. Hydrogen plays a vital role in powering stars through the proton-proton reaction and the CNO cycle nuclear fusion. COUNT 4
QSN1 What percent of normal matter is hydrogen? ANS1 75% QSN2 What percent of atoms is hydrogen? ANS2 90% QSN3 What 2 forms of mass is most of the universe consisted of? ANS3 dark matter and dark energy QSN4 Clouds of H2 form what? ANS4 stars