Aqueous `Cu^(2+)` ions are blue in colour, where as Aqueous `Zn^(2+)` ions are colourless. Why ?

Explanation

`rarr` electronic configuration of `Cu^(+2)` ion is `[Ar]4s^(0)3d^(9)`. It contains one unpaired electron due to presence of this unpaired electron aq. `Cu^(+2)` ions are blue in colour.
`rarr` Electronic configuration of `Zn^(+2)` ion is `[Ar] 4s^(0)3d^(10).` It contains no unpaired electrons, due to absence of unpaired electrons aq. `Zn^(+2)` ions are colourless.