70.Which of the following do you expect to be coloured and why? Cr+, Cu+?
Transition element exhibit colour due to d-d transition. This is possible only when d- subshell have unpaired electron. Cr+ is coloured because of the presence of partially filled d-orbitals (3d5 4s0) whereas Cu+ is colourless because of completely filled d-orbitals (3d10 4s0).