(a) Which metal in the first transition series (3d series) exhibits +1 oxidation state most frequently and why?
(b) Which of the following cations are coloured in aqueous solutions and why?
`Sc^(3+),V^(3+),Ti^(4+),Mn^(2+)(At. "no".Sc=21,V=23,Ti=22,Mn=25)`

Answer

(a) Copper exhibits `+1` oxidation state in the first series of transition metals because when one electron is ion the configuration become stable due fully filled `d^(10)` configuration .
(b) The configuration of the given metal ion can be given as
`Sc^(4+)-3d^(0) 4s^(0)` ; No unpaired electrons
`V^(3+)-3d^(2)4s^(0);2`unpaired electrons
`T^(3+)-3d^(2)4s^(0)`;No unpaired electron
`Mn^(2+)-3d^(5)4s^(0);5` unpaired electrons
out of these, only `Sc^(3+)` and `Ti^(4+)` are colourless. All other ion are coloured due to presence of unpaired electrons.