Which gas is NOT a noble gas?

The correct answer is nitrogen because it is a diatomic molecule (N₂) that is part of the atmospheric air we breathe and is not classified as a noble gas. Noble gases, such as argon, xenon, and neon, are found in Group 18 of the periodic table. They are characterized by having a full valence shell of electrons, which makes them largely unreactive and stable under standard conditions. Nitrogen, on the other hand, does not have this complete electron configuration and is chemically reactive, forming various compounds with other elements. This fundamental difference in their chemical properties and electron configuration clearly distinguishes nitrogen from the noble gases.