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Give reasons for the following.
Salts of cuprous (Cu⁺) ion are colourless whereas the salts of cupric (Cu²⁺) ion are coloured.
Salts of cuprous ($\text{Cu}^+$) ion are colourless whereas the salts of cupric ($\text{Cu}^{2+}$) ion are coloured.
Answer
Answer
Because $\mathrm{Cu^{2+}}$ ($3d^9$) has an unpaired electron and shows d-d transitions, absorbing visible light, whereas $\mathrm{Cu^{+}}$ ($3d^{10}$) has no unpaired electron and no d-d transition, so it is colourless.