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Assertion : Cuprous ion $\left(\mathrm{Cu}^{+}\right)$is colourless whereas cupric ion $\left(\mathrm{Cu}^{++}\right)$is blue in the aqueous solution.
Reason : Cuprous ion $\left(\mathrm{Cu}^{+}\right.$) has unpaired electrons while cupric ion $\left(\mathrm{Cu}^{++}\right.$) does not.
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Reason : Cuprous ion $\left(\mathrm{Cu}^{+}\right.$) has unpaired electrons while cupric ion $\left(\mathrm{Cu}^{++}\right.$) does not.
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The correct answer is:
If the assertion is true but the reason is false.
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.
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