Which group contains the noble gases?

• A. Group 18
• B. Group 7
• C. Group 2
• D. Group 1

Answer: (D)

A group is defined by the electrons in the outermost shell. Noble gases have a completely filled outer shell, which makes them exceptionally stable and largely unreactive. In the periodic table they occupy the far-right column, where each element has a full valence shell (eight electrons for most, helium having two). This full shell gives them high ionization energies and very little tendency to gain or lose electrons, so they exist as monatomic gases under standard conditions.

So the group that contains the noble gases is the far-right group on the periodic table. The other groups mentioned correspond to other families: the reactive nonmetals known as halogens sit just to the left of the noble gases, while the leftmost and next-to-left columns are the alkali metals and alkaline earth metals, respectively.