Among the following cations, the number of cations which will give characteristic precipitate in their identification tests with ${{\rm{K}}_4}\left[ {{\rm{Fe}}{{({\rm{CN}})}_6}} \right]$ is ________.
${\rm{C}}{{\rm{u}}^{2 + }},{\rm{F}}{{\rm{e}}^{3 + }},{\rm{B}}{{\rm{a}}^{2 + }},{\rm{C}}{{\rm{a}}^{2 + }},{\rm{NH}}_4^ + ,{\rm{M}}{{\rm{g}}^{2 + }},{\rm{Z}}{{\rm{n}}^{2 + }}$