Which complex is colourless in solution?

A.     ${\text{[Fe(}}{{\text{H}}_2}{\text{O}}{{\text{)}}_6}{\text{]C}}{{\text{l}}_2}$

B.     ${\text{[Ni(N}}{{\text{H}}_3}{{\text{)}}_6}{\text{]C}}{{\text{l}}_2}$

C.     ${\text{[Zn(}}{{\text{H}}_2}{\text{O}}{{\text{)}}_6}{\text{](N}}{{\text{O}}_3}{{\text{)}}_2}$

D.     ${{\text{K}}_3}[{\text{Co(CN}}{{\text{)}}_6}]$

C