# What is the only element that can form both a cation and an anion?

You are probably referring to hydrogen, which can form ${1}^{+}$ and ${1}^{-}$ ions.
However, there are other elements that can form both cations and anions, such as arsenic, which can form ${3}^{-}$, ${3}^{+}$, and ${5}^{+}$ ions; and tellurium, which can form ${2}^{-}$ and ${4}^{+}$ ions.