日韩欧美一区二区久久,999成人精品视频在线,国产精品亚洲а∨天堂2021,日韩一区二区不卡中文字幕,日韩欧美三区,欧美人与物videos新另类性,国产福利专区

At normal temperature and pressure, hydrogen is a gas that is extremely flammable, colorless, transparent, odorless, odorless, and difficult to dissolve in water. Hydrogen is the smallest known Density gas in the world. The Density of hydrogen is only 1/14 of that of air. That is, at 0 ° C, at a standard atmospheric pressure, the Density of hydrogen is 0.089g / L. Therefore, hydrogen can be used as a filling gas for airships and hydrogen balloons (because hydrogen is flammable and not very safe, airships are now filled with helium). Hydrogen is the substance with the smallest molecular weight and is mainly used as a reducing agent