Which of the following gases is not a noble gas?

Explanation

Noble gases are chemically inactive non-metals. They are located in group 18 of the periodic table. These substances extremely rarely form chemical compounds, as their outermost electron shell contains the maximum number of valence electrons, which is 8. Noble gases are the elements helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and the synthetically produced ununoctium (Uuo). These elements are colorless, odorless, tasteless, and non-flammable under standard conditions.