Which ion is colourless?1 pointA. [Sc (H2O)6]3+B. [Cr (H2O)6]3+C. [Fe (H2O)6]3+D. [Fe (CN)6]3–

The color of a complex ion depends on the transition of electrons between the d-orbitals of the central metal ion.

A. [Sc(H2O)6]3+: Scandium ion has a 3d0 configuration. There are no d-electrons for transitions and hence, it is colorless.

B. [Cr(H2O)6]3+: Chromium ion has a 3d3 configuration. The d-d transitions result in various colors.

C. [Fe(H2O)6]3+: Iron ion has a 3d5 configuration. The d-d transitions result in various colors.

D. [Fe(CN)6]3–: This is a complex ion with Iron. The color depends on the transitions of d-electrons.

So, the colorless ion among the given options is A. [Sc(H2O)6]3+.