1. Half filled or filled sub-shells are most stable so are favoured at expense of 4s sub-shell only containing 1 electron (see page for more info)
2. A tranistional element is defined as a d-block element forming one or more stable ions with incompletely filled d-orbitals e.g. zinc and scandium are not transitional metals because they can't form ions with partially filled d-orbitals
3. They form ions with partially filled d-orbitals which can absorb light 
4. green. therefore absorbs red approx 650nm
5. rust coloured gelatinous precipitate
6. dichlorotetraamminechromium(lll) ion
7. [Cu(H2O)6]2+(aq) + 4Cl-(aq) ---> [CuCl4]2-(aq) + 6H2O(l)
450nm Blue absorbed, Yellow observed (λ 600nm) so use blue filter - use graph to determine the ratio when colour is first fully yellow
[CuCl4]2-(aq) + 4NH3(aq) + 2H2O(l) ---> [Cu(NH3)4(H2O)2]2+(aq) + 4Cl-(aq)
580nm Yellow absorbed, Dark blue observed (λ 430nm)
use blue filter
8. 82.4%