Discovered only weeks after krypton and neon, this element has an atomic mass of 131 and was named for being "strange".
The hyperpolarized isotope of this element is used as a contrast agent in magnetic resonance imaging to visualize gas flow through the lung. The trioxide of this element undergoes violent decomposition at only 77 degrees Fahrenheit, making it a highly explosive oxidizing agent in the +6 oxidation state of this element. In fast atom bombardment, atoms of this element are used to create (*) ions in preparation for mass spectrometry.  One structure involving this element has two axial unbound electron pairs when this element bonds to four fluorines to form a square planar compound. Discovered only weeks after krypton and neon, this element has an atomic mass of 131 and was named for being "strange". For 10 points, name this noble gas below krypton on the periodic table, an element with symbol Xe.
The hyperpolarized isotope of this element is used as a contrast agent in magnetic resonance imaging to visualize gas flow through the lung.
xenon