出典:Wikipedia
出典:『Wikipedia』 (2011/07/31 00:24 UTC 版)
Hydrogen (
/ˈhaɪdrɵdʒɨn/ hy-drə-jin) is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly composed of hydrogen in its plasma state. Naturally occurring elemental hydrogen is relatively rare on Earth.
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