Question on Complex ions?

Question

Which of the following complex ions would absorb light with the longest wavelength.

A. [Co(H2O)6](2+)
B. [Co(NH3)6](2+)
C. [CoF6](4-)
D. [Co(CN)6](4-)
E. [Co(en)6](2+)

Answer 1

The ligands you list can be arranged in order of increasing energy of transitions that occur when they are present in a complex, from lowest to highest. The order is:

F- < OH2 < NH3 < en < CN-

The longest wavelength would be associated with the complex which has the lowest energy transition. That complex is C, [CoF6]4-.

Also, complex E probably doesn't exist because "en", or ethylenediamine, is a bidentate ligand and therefore occupies two coordination sites on the cobalt atom, instead of just one. You probably mean [Co(en)3]2+.

Answer 2

is it B?