Answer
See explanation below.
Work Step by Step
Given that three of the complex ions that are formed by Co3+ are [Co(H2O)6]3+, [Co(NH3)6]3+, and [CoF6]3-.The order of ligand-field strength is:
NH3>H2O>F-.
So this suggests that [Co(NH3)6]3+ absorbs higher energy light, then [Co(H2O)6]3+ and [CoF6]3-.This suggests that as [Co(NH3)6]3+ absorbs blue-green, it appears yellow-orange.[Co(H2O)6]3+ absorbs orange light and
appear blue.[CoF6]3- absorbs red light and appears green.
