Question

Assertion : Cuprous ion $(C{u}^{+})$ is colourless whereas cupric ion $(C{u}^{++})$ is blue in the aqueous solution.
Reason : Cuprous ion $(C{u}^{+})$ has unpaired electrons while cupric ion $(C{u}^{++})$ does not.

• A. If both assertion and reason are true and reason is a correct explanation of the assertion
• B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion
• C. If the assertion is true but the reason is false
• D. If both the assertion and reason are false

Answer 1

Answer: (C)

Cuprous ions $\left(C{u}^{+}\right)$ is colourless because it has no unpaired electrons in the $3d$ sub-shell as it has $3d^{10}$ configuration. The cupric ion $\left(C{u}^{++}\right)$ has one unpaired electron as it has configuration $3d^9$. 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 $\left(C{u}^{++}\right)$ in aqueous solution shows blue colour.