Which ion is colourless?

A.     ${{\text{[Sc(}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{)}}_{\text{6}}}{\text{]}}^{3 + }}$

B.     ${{\text{[Cr(}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{)}}_{\text{6}}}{\text{]}}^{3 + }}$

C.     ${{\text{[Fe(}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{)}}_{\text{6}}}{\text{]}}^{3 + }}$

D.     ${{\text{[Fe(CN}}{{\text{)}}_{\text{6}}}{\text{]}}^{3 - }}$

A