Assertion : Cuprous ion (Cu^ + ) is colourless whereas cupric ion...

Cuprous ions $\left(\mathrm{Cu}^{+}\right)$is colourless because it has no unpaired electrons in the $3 d$ sub-shell as it has $3 d^{10}$ configuration. The cupric ion $\left(\mathrm{Cu}^{++}\right)$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 $\left(\mathrm{Cu}^{++}\right)$in aqueous solution shows blue colour.