The term ONE OF THE NOBLE GASES refers to four elements in the periodic table: ARGON (5 letters), NEON (4 letters), XENON (5 letters) and RADON (5 letters). ARGON is a colorless, odorless gas that is the third most abundant element in the Earth's atmosphere. NEON is a colorless, odorless gas that is the second most abundant noble gas in the Earth's atmosphere. XENON is a colorless, odorless gas that is the fifth most abundant noble gas in the Earth's atmosphere. RADON is a radioactive, colorless, odorless gas that is the heaviest of the noble gases.