The van’ t Hoff factor (i) for a dilute aqueous solution of the strong electrolyte barium hydroxide is
3
Being a strong electrolyte, Ba(OH)2 undergoes 100% dissociation in a dilute aqueous solution,
Ba(OH)2(aq)→Ba2+aq+2OH−(aq)
Thus, van’t Hoff factor i = 3.