Question

which of the following can not be an ion? *
aluminum
hydrogen
carbon
bromine
krypton

Explanation:

Ions are formed when atoms gain or lose electrons. Krypton is a noble - gas with a full outer electron shell in its neutral state and is highly stable. It has a very low tendency to gain or lose electrons to form ions compared to the other elements listed. Aluminum can form $Al^{3 + }$ ions, hydrogen can form $H^{+}$ or $H^{-}$ ions, carbon can form various ions in organic and inorganic compounds, and bromine can form $Br^{-}$ ions.

Answer:

Krypton