Among the following, tri acidic base is

Acidity of a base:

Mono acidic base : 

A base which produces one hydroxyl ion by the ionization of one molecule of the base, is called as mono acidic base.

Ex: NaOH, KOH, NH₄OH

Diacidic base:
A base which produces two hydroxyl ion by the ionization of one molecule of the base, is called as diacidic base.
Ex:  $\mathrm{Ca}(\mathrm{OH}{)}_2,\mathrm{Mg}(\mathrm{OH}{)}_2,\mathrm{Cu}(\mathrm{OH}{)}_2,\mathrm{Zn}(\mathrm{OH}{)}_2,\mathrm{Fe}(\mathrm{OH}{)}_2$
Tri acidic base:
A base which produces three hydroxyl ions by the ionization of one molecule of the base is called a triacidic base.
Ex: $\mathrm{Fe}(\mathrm{OH}{)}_3,\mathrm{Al}(\mathrm{OH}{)}_3,\mathrm{Cr}(\mathrm{OH}{)}_3$