Helium is a chemical element with symbol He and atomic number 2. It is a rare atmospheric gas which is colorless, odorless, tasteless, nontoxic, nonflammable and only slightly soluble in water. The concentration of Helium in the atmosphere by volume percent is 5.24 x 10-4. Its boiling points and melting points are the lowest among all the elements and it exists only as a gas except in extremely cold conditions. 更多
