Is Na+ an acid or a base?

The large sodium ion, $N {a}^{+}$, is neither an acid nor a base in water.
The sodium has a fairly large charge to size ratio. It does not function effectively as a base. If sodium salts do have an effect on solution $p H$, it is because of the action of the gegenion, $C {O}_{3}^{2 -} . O {H}^{-} , {F}^{-}$, whatever.