How do quaternary ammonium hydroxides differ from quaternary ammonium chlorides in basicity?

Quaternary ammonium hydroxides are strong bases, whereas quaternary ammonium chlorides are salts and do not exhibit the same basic properties.

The difference lies in their chemical structure and reactivity. Quaternary ammonium hydroxides contain the hydroxide ion (${\text{OH}}^{-}$), which is a strong base, making the compound itself a strong base. In contrast, quaternary ammonium chlorides are the salt forms of these compounds, where the hydroxide ion has been replaced by a chloride ion (${\text{Cl}}^{-}$). Because the chloride ion is the conjugate base of a strong acid (hydrochloric acid), it is an extremely weak base, rendering the quaternary ammonium chloride neutral rather than basic.1

These hydroxides are also notable for their role in the Hofmann degradation, a reaction where they are heated to produce a tertiary amine and an alkene.2