The term 'Heavy Noble Gas' refers to two elements on the periodic table: XENON and RADON. XENON is a colorless, odorless, tasteless noble gas that is found in the Earth's atmosphere in trace amounts. RADON is a radioactive, colorless, odorless, tasteless noble gas that is formed as a result of the decay of uranium and thorium in rocks and soil. Both XENON and RADON are considered heavy noble gases due to their atomic weights, which are higher than those of the other noble gases.