Assertion : Cuprous ion ( Cu ⁺ ) is colourless whereas cupric ion ( Cu ⁺⁺ ) is blue in the aqueous solution. Reason : Cuprous ion ( Cu ⁺ . ) has unpaired electrons while cupric ion ( Cu ⁺⁺ . ) does not.

Step-by-step solution

Cuprous ions ( Cu ⁺ ) is colourless because it has no unpaired electrons in the 3 d sub-shell as it has 3 d¹⁰ configuration. The cupric ion ( Cu ⁺⁺ ) has one unpaired electron as it has configuration 3 d^9 . By absorbing the visible light, the unpaired electron can migrate from one set of d -orbitals to another under the applied field of water molecules. Hence, cupric ion ( Cu ⁺⁺ ) in aqueous solution shows blue colour.