Moments, colour and energy gaps

You will write functions for the magnetic moment of an ion, for its colour and for the energy gap that a colour matches.

The idea. For $d$ electrons, the unpaired electrons number $d$ if $d \le 5$ and $10 - d$ above that. The spin-only moment is $\sqrt{n(n+2)}$ BM. An ion is coloured only if it can make a d-d jump. A gap of $E$ kJ/mol absorbs a wavelength of $119\,627 / E$ nm.

Your tasks.

1. Complete unpaired(d) so that it returns the unpaired electrons of an ion with d electrons in $3d$.
2. Complete moment(n) so that it returns the spin-only moment, in BM, for n unpaired electrons.
3. Complete coloured(d) so that it returns True when a d-d jump is possible.
4. Complete wavelength(gap) so that it returns the wavelength in nm for a gap in kJ/mol.