Which compound is likely to be colourless?

A.     ${\text{[Zn(}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{)}}_{\text{6}}}{\text{]C}}{{\text{l}}_{\text{2}}}$

B.     ${{\text{[N}}{{\text{H}}_{\text{4}}}{\text{]}}_{\text{2}}}{\text{[Fe(}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{)}}_{\text{6}}}{\text{][S}}{{\text{O}}_{\text{4}}}{{\text{]}}_{\text{2}}}$

C.     ${{\text{K}}_{\text{3}}}{\text{[Co(CN}}{{\text{)}}_{\text{6}}}{\text{]}}$

D.     ${\text{[Ni(N}}{{\text{H}}_{\text{3}}}{{\text{)}}_{\text{6}}}{\text{][B}}{{\text{F}}_{\text{4}}}{{\text{]}}_{\text{2}}}$

A