The correct answer is Actinium. Explanation & Key Takeaways: Actinium: • It was discovered in the year 1899 by Andrew Debierne. • He extracted it from the uranium ore pitchblende (uranium oxide, U3O8) which occurs in trace amounts. • Actinium is a soft, silvery-white radioactive metal, it glows blue in the dark because its intense radioactivity excites the air around it. • Actinium is a very powerful source of alpha rays but is rarely used outside research. • Actinium used for research purposes is made by the neutron bombardment of radium-226. • Actinium also occurs naturally in uranium ores. Nobel Gasses: • Inert gases are nonmetals placed at the extreme right end of the periodic table. • They all together form the 18th group of the period table. • They have a stable electronic configuration i.e., all of their electronic orbitals are completely filled. • Nobel gasses are a group of chemical elements that do not interact with other elements in a manner. • General because their electron orbits are complete and filled with electrons. • Helium, Neon, Argon, Krypton, Xenon and Radon. • These elements are in the eighteenth groups of the periodic table. • Nobel gasses contain 0.93% of the atmospheric volume and 1.29% of its mass. Important Notes: Properties of Nobel Gasses: • Show as gases in room conditions. • No colour and no smell. • Have 8 electrons equivalent. • Produce vehicles only in special circumstances. • It is drawn from the air in liquefaction and distillation. • Found in the form of single-atom gases. • The very weak internal attraction between their atoms. • It has very low melting and boiling grades. Electronic Configuration of Noble gases. • He = 1s2 • Ne = [He]2s22p6 • Ar = [Ne]3s23p6 • Kr = [Ar]3d104s24p6 • Xe = [Kr]4d105s25p6 • Rd = [Xe]4f145d106s26p6 Related Concepts: • Xenon(Xe) gas is also known as stranger gas. • It is called 'STRANGER GAS' because the word 'XENON' means 'STRANGE' in Greek. • The noble gas Xenon possesses the highest melting point. • It was discovered by William Ramsay and Morris Travers in 1898. • It is more than 4.5 times heavier than air. • xenon is colorless, odorless, and tasteless. • It is used in instruments for radiation detection.